Dr.  Lillian  M.  Whiting 

PRESENTED  BY 
Dr.  Lillian  Berlier 


DARWIN,  AND  AFTER  DARWIN 

i 

THE    DARWINIAN    THEORY 


BY  THE  SAME  AUTHOR. 


DARWIN,  AND  AFTER  DARWIN.  An  Exposition  of  the 
Darwinian  Theory  and  a  Discussion  of  Post-Darwinian 
Questions. 

1.  THE  DARWINIAN  THEORY.    460  pages.    125  illustra- 

tions.    Cloth,  $2.00. 

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Lloyd  Morgan.     338  pages.     Cloth,  $1.50. 
Both  volumes  together,  83.00  net. 

THOUGHTS  ON  RELIGION.  Edited  by  Charles  Gore,  M. A., 
Canon  of  Westminster.  Second  Edition.  184  pages.  Cloth, 
gilt  top,  $1.25. 

AN  EXAMINATION  OF  WEISMANNISM.  236  pages.  Cloth, 
$i  oo. 


THE  OPEN  COURT  PUBLISHING  COMPANY, 
324  DEARBORN  STREET,  CHICAGO. 


LDARWIN,  AND  AFTER  DARWf^,TK 

FKYSfCfMr.  T.fEON 


AN  EXPOSITION  OF  THE  DARWINIAN  THEORY 

AND  A  DISCUSSION  OF 
POST-DARWINIAN  QUESTIONS 


*BY 
OMANES,  M.A.,  LL.D.,  F.R.S. 


I 

THE  DARWINIAN  THEORY 

(SECOND  EDITION) 


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THE  OPEN  COURT  PUBLISHING  COMPANY 
1896 


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The  Illustrations  of  this  book  (with  the  exception  of  the  Frontispiece  and  the 
colored  plate  facing  page  332)  are  copyrighted  under  the  title  "  Darwinism  Illus- 
trated." 

THE  OPEN  COURT  PUBLISHING  Co. 


JTIjf  ILaftrgitir  ^JJrras 

R.   R.   DONNELLEY   St   SONS  CO.,  CHICAGO. 


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PREFACE 


SEVERAL  years  ago  Lord  Rosebcry  founded,  in 
the  University  of  Edinburgh,  a  lectureship  on  '•  The 
Philosophy  of  Natural  History/'  and  I  was  invited  by 
the  Senatus  to  diliver  the  lectures.  This  invitation 
I  accepted,  and  subsequently  constituted  the  material 
of  my  lectures  the  foundation  of  another  cours?,  which 
was  given  in  the  Royal  Institution,  under  the  title 
"  Before  and  after  Darwin."  Here  the  course  extended 
over  three  years -namely  from  1888  to  1890.  The 
lectures  for  1 888  were  devoted  to  the  history  of  biology 
from  the  earliest  recorded  times  till  the  publication  of 
the  "  Origin  of  Species "  in  1 859  ;  the  lectures  for 
1889  dealt  with  the  theory  of  organic  evolution  up  to 
the  date  of  Mr.  Darwin's  death,  in  1882  ;  while 
those  of  the  third  year  discussed  the  further  develop- 
ments of  this  theory  from  that  date  till  the  close  of 
the  course  in  1890. 

It  is  from  these  two  courses — which  resembled  each 
other  in  comprising  between  thirty  and  forty  lectures 
but  differed  largely  in  other  respects — that  the  pre- 
sent treatise  has  grown.  Seeing,  however,  that  it  has 


vi  Preface. 

grown  much  beyond  the  bulk  of  the  original  lectures, 
I  have  thought  it  desirable  to  publish  the  whole  in 
the  form  of  three  separate  works.  Of  these  the  first 
—or  that  which  deals  with  the  purely  historical  side 
of  biological  science — may  be  allowed  to  stand  over 
for  an  indefinite  time.  The  second  is  the  one  which 
is  now  brought  out,  and  which,  as  its  sub-title  signifies, 
is  devoted  to  the  general  theory  of  organic  evolution 
as  this  was  left  by  the  stupendous  labours  of  Darwin. 
As  soon  as  the  translations  shall  have  been  completed, 
the  third  portion  will  follow  (probably  in  the  Autumn 
season),  under  the  sub-title,  "  Post-Darwinian  Ques- 
tions." 

As  the  present  volume  is  thus  intended  to  be  merely 
a  systematic  exposition  of  what  may  be  termed  the 
Darwinism  of  Darwin,  and  as  on  this  account  it  is 
likely  to  prove  of  more  service  to  general  readers  than 
to  professed  naturalists,  I  have  been  everywhere  care- 
ful to  avoid  assuming  even  the  most  elementary  know- 
ledge of  natural  science  on  the  part  of  those  to  whom 
the  exposition  is  addressed.  The  case,  however,  will 
be  different  as  regards  the  next  volume,  where  I  shall 
have  to  deal  with  the  important  questions  touching 
Heredity,  Utility,  Isolation,  &c.,  which  have  been 
raised  since  the  death  of  Mr.  Darwin,  and  which  are 
now  being  debated  with  such  salutary  vehemence  by 
the  best  naturalists  of  our  time. 

My  obligations  to  the  Senatus  of  the  University 
of  Edinburgh,  and  to  the  Board  of  Management  of 
the  Royal  Institution,  have  already  been  virtually 


Preface.  vii 

expressed ;  but  I  should  like  to  take  this  opportunity 
of  also  expressing  my  obligations  to  the  students  who 
attended  the  lectures  in  the  University  of  Edinburgh. 
For  alike  in  respect  of  their  large  numbers,  their 
keen  intelligence,  and  their  generous  sympathy,  the 
members  of  that  voluntary  class  yielded  a  degree  of 
stimulating  encouragement,  without  which  the  labour 
of  preparing  the  original  lectures  could  not  have  been 
attended  with  the  interest  and  the  satisfaction  that  I 
found  in  it.  My  thanks  are  also  due  to  Mr.  R.  E. 
Holding  for  the  painstaking  manner  in  which  he  has 
assisted  me  in  executing  most  of  the  original  drawings 
with  which  this  volume  is  illustrated  ;  and  likewise  to 
Messrs.  Macmillan  and  Co.  for  kindly  allowing  me 
to  reprint — without  special  acknowledgment  in  every 
case— certain  passages  from  an  essay  which  they 
published  for  me  many  years  ago,  under  the  title 
"  Scientific  Evidences  of  Organic  Evolution.  Lastly, 
I  must  mention  that  I  am  indebted  to  the  same  firm 
for  permission  to  reproduce  an  excellent  portrait  of 
Mr.  Darwin,  which  constitutes  the  frontispiece. 

G.  J.  R. 

CHRIST  CHURCH,  OXFORD, 
April  I9///,  1892. 


CONTENTS 


CHAPTER  I. 
INTRODUCTORY  . 


CHAPTER  II. 
CLASSIFICATION 23 

CHAPTER  III. 
MORPHOLOGY 50 

CHAPTER  IV. 
EMBRYOLOGY 98 

CHAPTER  V. 
PALAEONTOLOGY 156 

CHAPTER  VI. 
GEOGRAPHICAL  DISTRIBUTION 304 

CHAPTER  VII. 
THE  THEORY  OF  NATURAL  SELECTION 251 

CHAPTER  VIII. 
EVIDENCES  OF  THE  THEORY  OF  NATURAL  SELECTION       .        .    285 


x  Contents. 

CHAPTER  IX. 

PAGE 

CRITICISMS  OF  THE  THEORY  OF  NATURAL  SELECTION      .       .    333 

CHAPTER  X. 

THE   THEORY   OF    SEXUAL   SELECTION,   AND    CONCLUDING 

REMARKS ...    379 


APPENDIX  TO  CHAPTER  V 421 

NOTE  A  TO  PAGE  2^7 443 

NOTE  B  TO  PAGE  295 44=, 

NOTE  C  TO  PAGE  394 448 


INDEX 


45' 


LIST   OF    ILLUSTRATIONS 


PAGE 

FIG.  T.  Successive  forms  of  Paludina,  from  the  Tertiary  deposits 

ofSlavcnia 19 

2.  Skeleton  of  Seal 52 

3.  Skeleton  of  Greenland  Whule 53 

4.  Paddle  of  Whale  compared  with  Hand  ol  Man         .         .  54 

5.  Wing  of  Reptile,  Mammal,  and  Bird        ....  56 

6.  Skeleton  of  Dinorn is  gravis     .        .        .         .         .         .61 

7.  Hermit-crabs  compared  with  the  cocoa-nut  crab       .         .  64 

8.  Rudimentary  or  vestigial  hind-limbs  of  P)thon         .         .  67 
g.  Apteryx  Auslralu 69 

10.  Illustrations   of   the    nictitating    membiane    in    various 

animals  named .         -75 

11.  Rudimentary,  or  vestigial   and   useless,  muscles  of  the 

human  ear 76 

12.  Portrait  of  a  young  male  gorilla        .....  78 

13.  Portrait  of  a  young  male  child 79 

14.  An  infant,  three  weeks  old,  suppoiting  its  own  weight      .  81 

15.  Sacrum  of  Gorilla  compared  with  that  of  Man,  showing 

the  rudimentary  tail-bones  of  each       ....  82 

1 6.  Diagrammatic  outline  of  the  human  embryo  when  about 

seven  weeks  old 83 

17.  Front  and  back  view  of  adult  human  sacrum    ...  84 

1 8.  Appendix  vermiformis  in  Orang  and  in  Man    ...  85 

19.  The  same,  showing  variation  in  the  Orang       ...  85 

20.  Human  ear 86 

21.  1  cetus  of  an  Orang 87 

22.  Vestigial  characters  of  human  ears            ....  88 

23.  Hair-tracts  on  the  arms  and  hands  of  Man,  as  compared 

with  those  on  the  arms  and  hands  of  Chimpanzee        .  90 

24.  Molar  teeth  of  lower  jaw  in  Gorilla,  Orang,  and  Man        .  93 


xii  List  of  Illustrations. 

PAGE 

FIG.  25.  Perforation  of  the  humerus  (supra-condyloid  foramen)  in 
three  species  of  Quadrumana  where  it  normally  occurs, 
and  in  Man,  where  it  does  not  normally  occur  .  .  9=, 

26.  Antlers  of  stag,  showing  successive  addition  of  branches 

in  successive  years 100 

27.  Fission  of  a  Protozoon 107 

28.  Hydra  viridis,  partly  in  section 1 1 1 

29.  Successive  stages  in  the  division  of  the  ovum,  or  egg-cell, 

of  a  worm 113 

30.  Ovarian  ovum  of  a  Mammal  .         .         .         .         .121 

3 1 .  Amoeboid  movements  of  young  egg-cells        .         .         .122 

32.  Human  ovum,  mature  and  greatly  magnified  .         .     173 
33-  Stages  in  the  formation  of  the  polar  bodies  in  the  ovum  of 

a  star-fish   .         .         .         .         .    ••    ,         .         .         .     I2;'; 

34.  Fertilization  of  the  ovum  of  an  echinoderm    .         .         .126 

35.  Fertilization  of  the  ovum  of  a  star-fish    ....     127 

36.  Karyolunesis  of  a  typical  tissue-cell  (epithelium  of  Sala- 

mander)     .        , 129 

37.  Study  of  successive  changes  taking  place  in  the  nucleus 

of  an  epithelium-cell,  preparatory  to  division  of  the  cell     131 

38.  Formation  and  conjugation  of  the  pronuclei  in  Ascaris 

megalocephala 132,  133 

39.  Segmentation  of  ovum 135 

40.  The  contents  of  an  ovum  in  an  advanced  stage  of  segmen- 

tation, drawn  in  perspective         .         .        .         .         .     1 35 

41.  Formation  of  the  gastrnla  of  Amfhioxus       .         .        .137 

42.  Gastrulation          ,        , 138 

43.  Gartrula  of  a  Chalk  Sponge 139 

44.  Prophysema  pri m ordiale,  an  extant  gasti  sea.- form    .         .140 

45.  Ideal  primitive  vertebrate,  seen  from  the  left  side   .         .143 

46.  The  same  in  transverse  section  through  the  ovaries         .     144 

47.  Amphioxus  lanccolatus 145 

48.  Balanoglossus 148 

49.  A  large  Sea-lamprey  (j'elromyzon  marinus)  .         .         .     148 

50.  Adult  Shark  (Carcharias  melanopterus}          .        .         .149 

51.  Diagram  of  heart  and  gill-arches  of  a  fish       .         .         .150 

52.  One  gill-arch,  with  branchial  fringe  attached          .        .     150 
53-  Diagram  of  heart  and  gill-arches  in  a  lizard    .         .         .150 

54.  Ideal  diagram  of  primitive  gill- or  aortic- arches    .         .151 

55.  The  same,  modified  for  a  bird 151 

56.  The  same,  modified  for  a  mammal  .     uu 


List  of  Illustrations. 


PAGE 

FIG.  57.  A  series  of  embryos  at  three  comparable  and  progressive 
stages  of  development,  representing  each  of  the  classes 
of  vertebrated  animals  below  the  Mammalia  .  .  152 

58.  Another  series  of  embryos,  also  at  three  comparable  and 

progressive  stages  of  development,  representing  four  dif- 
ferent divisions  of  the  class  Mammalia         .         .         •     '5i 

59.  Diagram  of  geological  succession  of  the  classes  of  the 

Animal  Kingdom        .         .         .         .         .         .         .165 

60.  Skull  of  Oreodon  Culbertsoni 167 

61,62.  Horns  of  Cervus  dicroccrn.-       .....     168 

63.  „  C.  matheronis 168 

64.  „  C.pardinensis 168 

65.  „  C.  issiodorensis 168 

66.  „  C.  Sedgwickii 168 

67.  Successive  stages  in  the  development  of  an  existing  Deer's 

Antlers 169 

68.  Homocercal  tail 169 

69.  Heterocercal  tail 170 

70.  Vertebrated  but  symmetrical  fin  (diphycercal)         .         .170 

71.  Tail  of  Archaopteryx 171 

72.  Tail  of  modern  .Bird 171 

73.  Archaopteiyx  macura,  restored       .         .         .         .         .172 

74.  Skeleton  of  Polar  Bear 174 

75.  Skeleton  of  Lion 175 

76.  Anterior  limb  of  Man,  Dog,  Hog,  Sheep,  and  Horse      .     176 

77.  Posterior  limb  of  Man,  Monkey,  Dog,  Sheep,  and  Horse     177 

78.  Posterior  limb  of  Baptanodon  disctis,  and  anterior  limb  of 

Chelydra  serpentina    .         .         .         .         .         .         .179 

79.  Paddle  of  a  Whale 180 

80.  Fossil  skeleton  of  P/unacodus  primtevus          .         .         .184 

81.  Bones  of  the  foot  of  four  different  forms  of  the  perisso- 

dactyl  type 186 

82    Bonei  of  the  foot  of  four  different  forms  of  the  arliodactyl 

type 187 

83.  Feet  and  teeth  in  fossil  pedigree  of  the  Horse          .         .189 

84.  ralaoiherinm.  (Lower  Tertiary  of  Paris  Basin)       .         .190 

85.  Hipparion.  (New  World  Pliocene)         .         .         .         .192 

86.  Comparative  series  of  Brains  ......     194 

87.  Ideal  section  through  all  the  above  stages       .         .         .     195 

88.  Skulls  of  Canadian  Stag,  Cervalces  Atnericamis,  and  Elk     198 

89.  Transmutations  of  Planorbis  ......     200 


xiv  List  of  Illustrations. 

PAGE 

FIG.  90.  Transformation  of  Strombus 202 

91.  Pigeons.     Drawn  from  life 298 

92.  Pigeons  (continued).    Drawn  from  life  ....  299 

93.  Fowls.     Drawn  from  life 3°° 

94.  Fowls  (continued).    Drawn  from  life     .         .         .         .301 

95.  Pair  of  Japanese  Fowls,  long-tailed  breed        .         .         .  302 

96.  Cnnaries.     Drawn  from  life   ......  303 

97.  Sebastopol,  or  Frizzled  Goose 304 

9$.  The  Dingo,  or  wild  dog  of  Australia      ....  304 

99.  Dogs.    Drawn  from  life 305 

100.  Dogs  (cont i ntied).      Drawn  from  life    ....  306 

101.  The  Hairless  Dog  of  Japan 307 

102.  The  skull  of  a  Bull-dog  compared  with  that  of  a  Deer- 

hound         ........         .         .  307 

103.  Rabbits.     Drawn  from  life 308 

104.  Horses.     Drawn  from  life 309 

105.  Sheep.     Drawn  from  life 310 

106.  Cattle.     Drawn  from  life 311 

107.  Wild  Boar  contrasted  with  a  modern  Domesticated  Pig  .  312 

108.  Seasonal  changes  of  colour  in  Ptarmigan  (Lagofus  mntus)  31 7 

109.  (Edicnemus  crepitans,  showing  the  instinctive  attitude  of 

concealment 320 

no.  Imitati%-e  forms  and  colours  in  insects     ....  322 

111.  The  larva  of  Puss  Moth  (Cerura  vinuta)       .         .        .325 

1 1 2.  The  larva  of  Puss  Moth  in  disturbed  attitude          .         .  326 

113.  Three  cases  of  mimicry 328 

1 14.  Two  further  cases  of  mimicry ;  flies  resembling  a  wasp  in 

the  one  and  a  bee  in  the  other 329 

1 15.  A  case  of  mimicry  where  a  non-venomous  species  of  snake 

resembles  a  venomous  one 330 

1 16.  A  case  of  mimicry  where  a  homopterous  resembles  a  leaf- 

cutting  ant 332 

117.  Feather-footed  pigeon 359 

1 1 8.  Kaia  radiata 368 

119.  Electric  organ  of  the  Skate 369 

120.  Electric  cells  of  Raia  radiata 370 

121.  The  Garden  Bower- bird  (Amblyornis  inornatd)      .         .  382 

122.  Courtship  of  Spiders 388 

123.  Courtship  of  Spiders  (continued} 389 

124.  The  Bell-bird  (Chasmorhynchus  niveus)         .         .         .396 

1 25.  C.  tricarunculatus 


SECTION   I 

EVOLUTION 


DARWIN,  AND  AFTER  DARWIN. 

CHAPTER    I. 

INTRODUCTORY. 

AMONG  the  many  and  unprecedented  changes  that 
have  been  wrought  by  Mr.  Darwin's  work  on  the  Origin 
of  Species,  there  is  one  which,  although  second  in  im- 
portance to  no  other,  has  not  received  the  attention 
which  it  deserves.  I  allude  to  the  profound  modifi- 
cation which  that  work  has  produced  on  the  ideas  of 
naturalists  with  regard  to  method. 

Having  had  occasion  of  late  years  somewhat  closely 
to  follow  the  history  of  biological  science,  I  have  every- 
where observed  that  progress  is  not  so  much  marked 
by  the  march  of  discovery  per  se,  as  by  the  altered 
views  of  method  which  the  march  has  involved.  If 
we  except  what  Aristotle  called  "  the  first  start "  in 
himself,  I  think  one  may  fairly  say  that  from  the  re- 
juvenescence of  biology  in  the  sixteenth  century  to 
the  stage  of  growth  which  it  has  now  reached  in  the 
nineteenth,  there  is  a  direct  proportion  to  be  found 
between  the  value  of  work  done  and  the  degree  in 
which  the  worker  has  thereby  advanced  the  true 
conception  of  scientific  working.  Of  course,  up  to  a 
*  B 


2  Darwin,  and  after  Darwin. 

certain  point,  it  is  notorious .  that  the  revolt  against 
the  purely  "subjective  methods"  in  the  sixteenth 
century  revived  the  spirit  of  inductive  research  as  this 
had  been  left  by  the  Greeks ;  but  even  with  regard 
to  this  revolt  there  are  two  things  which  I  should 
like  to  observe. 

In  the  first  place,  it  seems  to  me,  an  altogether 
disproportionate  value  has  been  assigned  to  Bacon's 
share  in  the  movement.  At  most,  I  think,  he  deserves 
to  be  regarded  but  as  a  literary  exponent  of  the  Zeit- 
geist of  his  century.  Himself  a  philosopher,  as  dis- 
tinguished from  a  man  of  science,  whatever  influence 
his  preaching  may  have  had  upon  the  general  public,  it 
seems  little  short  of  absurd  to  suppose  that  it  could 
have  produced  any  considerable  effect  upon  men  who 
were  engaged  in  the  practical  work  of  research.  And 
those  who  read  the  Novum  Organon  with  a  first-hand 
knowledge  of  what  is  required  for  such  research  can 
scarcely  fail  to  agree  with  his  great  contemporary 
Harvey,  that  he  wrote  upon  science  like  a  Lord 
Chancellor. 

The  second  thing  I  should  like  to  observe  is,  that 
as  the  revolt  against  the  purely  subjective  methods 
grew  in  extent  and  influence  it  passed  to  the  opposite 
extreme,  which  eventually  became  only  less  deleterious 
to  the  interests  of  science  than  was  the  bondage  of 
authority,  and  addiction  to  a  priori  methods,  from 
which  the  revolt  had  set  her  free.  For,  without  here 
waiting  to  trace  the  history  of  this  matter  in  detail, 
I  think  it  ought  now  to  be  manifest  to  everyone  who 
studies  it,  that  up  to  the  commencement  of  the  present 
century  the  progress  of  science  in  general,  and  of 
natural  history  in  particular,  was  seriously  retarded  by 


Introductory.  3 

what  may  be  termed  the  Bugbear  of  Speculation.  Fully 
awakened  to  the  dangers  of  web-spinning  from  the 
ever-fertile  resources  of  their  own  inner  consciousness, 
naturalists  became  more  and  more  abandoned  to  the 
idea  that  their  science  ought  to  consist  in  a  mere 
observation  of  facts,  or  tabulation  of  phenomena, 
without  attempt  at  theorizing  upon  their  philosophical 
import.  If  the  facts  and  phenomena  presented  any 
such  import,  that  was  an  affair  for  men  of  letters  to 
deal  with  ;  but,  as  men  of  science,  it  was  their  duty  to 
avoid  the  seductive  temptations  of  the  world,  the  flesh, 
and  the  devil,  in  the  form  of  speculation,  deduction, 
and  generalization. 

I  do  not  allege  that  this  ideal  of  natural  history  was 
either  absolute  or  universal  ;  but  there  can  be  no 
question  that  it  was  both  orthodox  and  general. 
Even  Linnaeus  was  express  in  his  limitations  of  true 
scientific  work  in  natural  history  to  the  collecting  and 
arranging  of  species  of  plants  and  animals.  In  ac- 
cordance.with  this  view,  the  status  of  a  botanist  or  a 
zoologist  was  estimated  by  the  number  of  specific 
names,  natural  habitats,  &c.,  which  he  could  retain  in 
.his  memory,  rather  than  by  any  evidences  which  he 
might  give  of  intellectual  powers  in  the  way  of  con- 
structive thought.  At  the  most  these  powers  might 
legitimately  exercise  themselves  only  in  the  direction 
of  taxonomic  work ;  and  if  a  Hales,  a  Haller,  or  a 
Hunter  obtained  any  brilliant  results  in  the  way  of 
observation  and  experiment,  their  merit  was  taken  to 
consist  in  the  discovery  of  facts  per  se :  not  in  any 
endeavours  they  might  make  in  the  way  of  combining 
their  facts  under  general  principles.  Even  as  late  in 
the  day  as  Cuvier  this  ideal  was  upheld  as  the  strictly 
B  2 


4  Darwin,  and  after  Darwin. 

legitimate  one  for  a  naturalist  to  follow ;  and  although 
Cuvier  himself  was  far  from  being  always  loyal  to  it, 
he  leaves  no  doubt  regarding  the  estimate  in  which  he 
held  the  still  greater  deviations  of  his  colleagues,  St. 
Hilaire  and  Lamarck. 

Now,  these  traditional  notions  touching  the  severance 
between  the  facts  of  natural  history  and  the  philosophy 
of  it,  continued  more  or  less  to  dominate  the  minds  of 
naturalists  until  the  publication  of  the  Origin  of 
Species,  in  1859.  Then  it  was  that  an  epoch  was 
marked  in  this  respect,  as  in  so  many  other  respects 
where  natural  history  is  concerned.  For,  looking  to 
the  enormous  results  which  followed  from  a  deliberate 
disregard  of  such  traditional  canons  by  Darwin,  it  has 
long  since  become  impossible  for  naturalists,  even  of 
the  strictest  sect,  not  to  perceive  that  their  previous 
bondage  to  the  law  of  a  mere  ritual  has  been  for  ever 
superseded  by  what  verily  deserves  to  be  regarded  as 
a  new  dispensation.  Yet  it  cannot  be  said,  or  even  so 
much  as  suspected,  that  Darwin's  method  iiv  any  way 
resembled  that  of  pre-scientific  days,  the  revolt  against 
which  led  to  the  straight-laced — and  for  a  long  time 
most  salutary— conceptions  of  method  that  we  have- 
just  been  noticing.  Where,  then,  is  the  difference? 
To  me  it  seems  that  the  difference  is  as  follows ;  and, 
if  so,  that  not  the  least  of  our  many  obligations  to 
Darwin  as  the  great  organizer  of  biological  science 
arises  from  his  having  clearly  displayed  the  true 
principle  which  ought  to  govern  biological  research. 

To  begin  with,  he  nowhere  loses  sight  of  the 
primary  distinction  between  fact  and  theory  ;  so  that, 
thus  far,  he  loyally  follows  the  spirit  of  revolt  against 
subjective  methods.  But,  while  always  holding  this 


Introductory.  5 

distinction  clearly  in  view,  his  idea  of  the  scientific  use 
of  facts  is  plainly  that  of  furnishing  legitimate  material 
for  the  construction  of  theories.  Natural  history  is 
not  to  him  an  affair  of  the  herbarium  or  the  cabinet. 
The  collectors  and  the  species-framers  are,  as  it  were, 
his  diggers  of  clay  and  makers  of  bricks :  even  the 
skilled  observers  and  the  trained  experimentalists  are 
his  mechanics.  Valuable  as  the  work  of  all  these  men 
is  in  itself,  its  principal  value,  as  he  has  finally  de- 
monstrated, is  that  which  it  acquires  in  rendering 
possible  the  work  of  the  architect.  Therefore,  although 
he  has  toiled  in  all  the  trades  with  his  own  hands,  and 
in  each  has  accomplished  some  of  the  best  work  that 
has  ever  been  done,  the  great  difference  between  him 
and  most  of  his  predecessors  consists  in  this, — that 
while  to  them  the  discovery  or  accumulation  of  facts 
was  an  end,  to  him  it  is  the  means.  In  their  eyes  it 
was  enough  that  the  facts  should  be  discovered  and 
recorded.  In  his  eyes  the  value  of  facts  is  due  to 
their  power  of  guiding  the  mind  to  a  further  discovery 
of  principles.  And  the  extraordinary  success  which 
attended  his  work  in  this  respect  of  generalization 
immediately  brought  natural  history  into  line  with  the 
other  inductive  sciences,  behind  which,  in  this  most 
important  of  all  respects,  she  has  so  seriously  fallen. 
For  it  was  the  Origin  of  Species  which  first  clearly 
revealed  to  naturalists  as  a  class,  that  it  was  the  duty 
of  their  science  to  take  as  its  motto,  what  is  really  the 
motto  of  natural  science  in  general, 

Felix  qui  potuit  rerum  cognoscere  causas. 

Not  facts,  then,  or  phenomena,  but  causes  or  prin- 
ciples, are  the  ultimate  objects  of  scientific  quest.  It 
remains  to  ask,  How  ought  this  quest  to  be  prosecuted  ? 


6  Darwin,  and  after  Darwin. 

Well,  in  the  second  place,  Darwin  has  shown  that 
next  only  to  the  importance  of  clearly  distinguishing 
between  facts  and  theories  on  the  one  hand,  and  of 
clearly  recognising  the  relation  between  them  on  the 
other,  is  the  importance  of  not  being  scared  by  the 
Bugbear  of  Speculation.  The  spirit  of  speculation  is 
the  same  as  the  spirit  of  science,  namely,  as  we  have 
just  seen,  a  desire  to  know  the  causes  of  things.  The 
hypotheses  non  fingo  of  Newton,  if  taken  to  mean  what 
it  is  often  understood  as  meaning,  would  express 
precisely  the  opposite  spirit  from  that  in  which  all 
scientific  research  must  necessarily  take  its  origin. 
For  if  it  be  causes  or  principles,  as  distinguished  from 
facts  or  phenomena,  that  constitute  the  final  aim  of 
scientific  research,  obviously  the  advancement  of  such 
research  can  be  attained  only  by  the  framing  of 
hypotheses.  And  to  frame  hypotheses  is  to  specu- 
late. 

Therefore,  the  difference  between  science  and  specu- 
lation is  not  a  difference  of  spirit  ;  nor,  thus  far,  is  it 
a  difference  of  method.  The  only  difference  between 
them  is  in  the  subsequent  process  of  verifying  hypo- 
theses. For  while  speculation,  in  its  purest  form,  is 
satisfied  to  test  her  explanations  only  by  the  degree 
in  which  they  accord  with  our  subjective  ideas  of  prob- 
ability— or  with  the  "  Illative  Sense"  of  Cardinal  New- 
man,— science  is  not  satisfied  to  rest  in  any  explanation 
as  final  until  it  shall  have  been  fully  verified  by  an 
appeal  to  objective  proof.  This  distinction  is  now  so 
well  and  so  generally  appreciated  that  I  need  not 
dwell  upon  it.  Nor  need  I  wait  to  go  into  any  details 
with  regard  to  the  so-called  canons  of  verification. 
My  only  object  is  to  make  perfectly  clear,  first,  that 


Introductory.  7 

in  order  to  have  any  question  to  put  to  the  test  of 
objective  verification,  science  must  already  have  so  far 
employed  the  method  of  speculation  as  to  have  framed 
a  question  to  be  tested  ;  and,  secondly,  that  the  point 
where  science  parts  company  with  speculation  is  the 
point  where  this  testing  process  begins. 

Now,  if  these  things  are  so,  there  can  be  no  doubt 
that  Darwin  was  following  the  truest  method  of  induc- 
tive research  in  allowing  any  amount  of  latitude  to  his 
speculative  thought  in  the  direction  of  scientific  theo- 
rizing. For  it  follows  from  the  above  distinctions  that 
the  danger  of  speculation  does  not  reside  in  the  width 
of  its  range,  or  even  in  the  impetuosity  of  its  vehe- 
mence. Indeed,  the  wider  its  reach,  and  the  greater  its 
energy,  the  better  will  it  be  for  the  interests  of  science. 
The  only  danger  of  speculation  consists  in  its  momen- 
tum being  apt  to  carry  away  the  mind  from  the  more 
laborious  work  of  adequate  verification;  and  therefore 
a  true  scientific  judgment  consists  in  giving  a  free 
rein  to  speculation  on  the  one  hand,  while  holding 
ready  the  break  of  verification  with  the  other.  Now, 
it  is  just  because  Darwin  did  both  these  things  with 
so  admirable  a  judgment,  that  he  gave  the  world  of 
natural  history  so  good  a  lesson  as  to  the  most  effec- 
tual way  of  driving  the  chariot  of  science. 

This  lesson  we  have  now  all  more  or  less  learnt  to 
profit  by.  Yet  no  other  naturalist  has  proved  himself 
so  proficient  in  holding  the  balance  true.  For  the 
most  part,  indeed,  they  have  now  all  ceased  to  con- 
found the  process  of  speculation  per  se  with  the  danger 
of  inadequate  verification  ;  and  therefore  the  old  ideal 
of  natural  history  as  concerned  merely  with  collecting 
species,  classifying  affinities,  and,  in  general,  tabulating 


8  Darwin,  and  after  Darwin. 

facts,  has  been  well-nigh  universally  superseded.  But 
this  great  gain  has  been  attended  by  some  measure  of 
loss.  For  while  not  a  few  naturalists  have  since  erred 
on  the  side  of  insufficiently  distinguishing  between  fully 
verified  principles  of  evolution  and  merely  specula- 
tive deductions  therefrom,  a  still  larger  number  have 
formed  for  themselves  a  Darwinian  creed,  and  regard 
any  further  theorizing  on  the  subject  of  evolution  as 
ipso  facto  unorthodox. 

Having  occupied  the  best  years  of  my  life  in 
closely  studying  the  literature  of  Darwinism,  I  shall 
endeavour  throughout  the  following  pages  to  avoid 
both  these  extremes.  No  one  in  this  generation  is 
able  to  imitate  Darwin,  either  as  an  observer  or  a 
generalizer.  But  this  does  not  hinder  that  we  should 
all  so  far  endeavour  to  follow  his  method,  as  always  to 
draw  a  clear  distinction,  not  merely  between  observa- 
tion and  deduction,  but  also  between  degrees  of 
verification.  At  all  events,  my  own  aim  will  every- 
where be  to  avoid  dogmatism  on  the  one  hand,  and 
undue  timidity  as  regards  general  reasoning  on  the 
other.  For  everything  that  is  said  justification  will 
be  given  ;  and,  as  far  as  prolonged  deliberation  has 
enabled  me  to  do  so,  the  exact  value  of  such  justifica- 
tion will  be  rendered  by  a  statement  of  at  least  the 
main  grounds  on  which  it  rests.  The  somewhat 
extensive  range  of  the  present  treatise,  however,  will 
not  admit  of  my  rendering  more  than  a  small  percen- 
tage of  the  facts  which  in  each  case  go  to  corroborate 
the  conclusion.  But  although  a  great  deal  must  thus 
be  necessarily  lost  on  the  one  side,  I  am  disposed  to 
think  that  more  will  be  gained  on  the  other,  by 
presenting,  in  a  terser  form  than  would  otherwise  be 


Introductory.  9 

possible,  the  whole  theory  of  organic  evolution  as  I 
believe  that  it  will  eventually  stand.  My  endeavour, 
therefore,  will  be  to  exhibit  the  general  structure  of 
this  theory  in  what  I  take  to  be  its  strictly  logical 
form,  rather  than  to  encumber  any  of  its  parts  by  a 
lengthy  citation  of  facts.  Following  this  method,  I 
shall  in  each  case  give  only  what  I  consider  the  main 
facts  for  and  against  the  positions  which  have  to  be 
argued  ;  and  in  most  cases  I  shall  arrange  the  facts 
in  two  divisions,  namely,  first  those  of  largest  gener- 
ality, and  next  a  few  of  the  most  special  character 
that  can  be  found. 

As  explained  in  the  Preface,  the  present  instalment 
of  the  treatise  is  concerned  with  the  theory  of  evolu- 
tion, from  the  appearance  of  the  Origin  of  Species  in 
1859,  to  the  death  of  its  author  in  1882;  while  the 
second  part  will  be  devoted  to  the  sundry  post- 
Darwinian  questions  which  have  arisen  in  the  sub- 
sequent decade.  To  the  possible  criticism  that  a 
disproportionate  amount  of  space  will  thus  be  allotted 
to  a  consideration  of  these  post-Darwinian  questions, 
I  may  furnish  in  advance  the  following  reply. 

In  the  first  place,  besides  the  works  of  Darwin 
himself,  there  are  a  number  of  others  which  have 
already  and  very  admirably  expounded  the  evidences, 
both  of  organic  evolution  as  a  fact,  and  of  natural 
selection  as  a  cause.  Therefore,  in  the  present 
treatise  it  seemed  needless  to  go  beyond  the  ground 
which  was  covered  by  my  original  lectures,  namely,  a 
condensed  and  connected,  while  at  the  same  time 
a  critical  statement  of  the  main  evidences,  and  the 
main  objections,  which  have  thus  far  been  published 
with  reterence  to  the  distinctively  Darwinian  theory. 


io  Darwin,  and  after  Darwin. 

Indeed,  while  re-casting  this  portion  of  my  lectures 
for  the  present  publication,  I  have  felt  that  criticism 
might  be  more  justly  urged  from  the  side  of  im- 
patience at  a  reiteration  of  facts  and  arguments 
already  so  well  known.  But  while  endeavouring,  as 
much  as  possible,  to  avoid  overlapping  the  previous 
expositions,  I  have  not  carried  this  attempt  to  the 
extent  of  damaging  my  own,  by  omitting  any  of  the 
more  important  heads  of  evidence  ;  and  I  have  sought 
to  invest  the  latter  with  some  measure  of  novelty  by 
making  good  what  appears  to  me  a  deficiency  which 
has  hitherto  obtained  in  the  matter  of  pictorial  illus- 
tration. In  particular,  there  will  be  found  a  tolerably 
extensive  series  of  woodcuts,  serving  to  represent  the 
more  important  products  of  artificial  selection.  These, 
like  all  the  other  original  illustrations,  have  been 
drawn  either  direct  from  nature  or  from  a  comparative 
study  of  the  best  authorities.  Nevertheless,  I  desire 
it  to  be  understood  that  the  first  part  of  this  treatise 
is  intended  to  retain  its  original  character,  as  a  merely 
educational  exposition  of  Darwinian  teaching— an 
exposition,  therefore,  which,  in  its  present  form, 
may  be  regarded  as  a  compendium,  or  hand-book, 
adapted  to  the  requirements  of  a  general  reader,  or 
biological  student,  as  distinguished  from  those  of  a 
professed  naturalist. 

The  case,  however,  is  different  with  the  second 
instalment,  which  will  be  published  at  no  very  distant 
date.  Here  I  have  not  followed  with  nearly  so  much 
closeness  the  material  of  my  original  lectures.  On 
the  contrary,  I  have  had  in  view  a  special  class  of 
readers  ;  and,  although  I  have  tried  not  altogether  to 
sacrifice  the  more  general  class,  I  shall  desire  it  to  be 


Introductory.  I  \ 

understood  that  I  am  there  appealing  to  naturalists 
who  are  specialists  in  Darwinism.  One  must  say 
advisedly,  naturalists  who  are  specialists  in  Dar- 
winism, because,  while  the  literature  of  Darwinism 
has  become  a  department  of  science  in  itself,  there 
are  nowadays  many  naturalists  who,  without  having 
paid  any  close  attention  to  the  subject,  deem  them- 
selves entitled  to  hold  authoritative  opinions  with 
regard  to  it.  These  men  may  have  done  admirable 
work  in  other  departments  of  natural  history,  and  yet 
their  opinions  on  such  matters  as  we  shall  hereafter 
have  to  consider  may  be  destitute  of  value.  As  there 
is  no  necessary  relation  between  erudition  in  one 
department  of  science  and  soundness  of  judgment 
in  another,  the  mere  fact  that  a  man  is  distinguished 
as  a  botanist  or  zoologist  does  not  in  itself  qualify  him 
as  a  critic  where  specially  Darwinian  questions  are 
concerned.  Thus  it  happens  now,  as  it  happened 
thirty  years  ago,  that  highly  distinguished  botanists 
and  zoologists  prove  themselves  incapable  as  judges 
of  general  reasoning.  It  was  Darwin's  complaint  that 
for  many  years  nearly  all  his  scientific  critics  either 
could  not,  or  would  not,  understand  what  he  had 
written — and  this  even  as  regarded  the  fundamental 
principles  of  his  theory,  which  with  the  utmost  clear- 
ness he  had  over  and  over  again  repeated.  Now  the 
only  difference  between  such  naturalists  and  their 
successors  of  the  present  day  is,  that  the  latter  have 
grown  up  in  a  Darwinian  environment,  and  so,  as 
already  remarked,  have  more  or  less  thoughtlessly 
adopted  some  form  of  Darwinian  creed.  But  this 
scientific  creed  is  not  a  whit  less  dogmatic  and 
intolerant  than  was  the  more  theological  one  which  it 


12  Darwin,  and  after  Darwin. 

has  supplanted  ;  and  while  it  usually  incorporates  the 
main  elements  of  Darwin's  teaching,  it  still  more 
usually  comprises  gross  perversions  of  their  conse- 
quences. All  this  I  shall  have  occasion  more  fully 
to  show  in  subsequent  parts  of  the  present  work  ;  and 
allusion  is  made  to  the  matter  here  merely  for  the 
sake  of  observing  that  in  future  I  shall  not  pay 
attention  to  unsupported  expressions  of  opinion  from 
any  quarter :  I  shall  consider  only  such  as  are  accom- 
panied with  some  statement  of  the  grounds  upon 
which  the  opinion  is  held.  And,  even  as  thus  limited, 
I  do  not  think  it  will  be  found  that  the  following 
exposition  devotes  any  disproportional  amount  of 
attention  to  the  contemporary  movements  of  Dar- 
winian thought,  seeing,  as  we  shall  see,  how  active 
scientific  speculation  has  been  in  the  field  of  Dar- 
winism since  the  death  of  Mr.  Darwin. 

Leaving,  then,  these  post-Darwinian  questions  to 
be  dealt  with  subsequently,  I  shall  now  begin  a 
systematic  rfeumJ  of  the  evidences  in  favour  of  the 
Darwinian  theory,  as  this  was  left  to  the  world  by 
Darwin  himself. 

There  is  a  great  distinction  to  be  drawn  between 
the  fact  of  evolution  and  the  manner  of  it,  or  between 
the  evidence  of  evolution  as  having  taken  place  some- 
how, and  the  evidence  of  the  causes  which  have  been 
concerned  in  the  process.  This  most  important 
distinction  is  frequently  disregarded  by  popular 
writers  on  Darwinism  ;  and,  therefore,  in  order  to 
mark  it  as  strongly  as  possible,  I  will  effect  a  com- 
plete separation  between  the  evidence  which  we  have 
of  evolution  as  a  fact,  and  the  evidence  which  we  have 


Introductory.  1 3 

as  to  its  method.  In  other  words,  not  until  I  shall 
have  fully  considered  the  evidence  of  organic  evolu- 
tion as  a  process  which  somehow  or  another  has 
taken  place,  will  I  proceed  to  consider  how  it  has 
taken  place,  or  the  causes  which  Darwin  and  others 
have  suggested  as  having  probably  been  concerned  in 
this  process. 

Confining,  then,  our  attention  in  the  first  instance 
to  a  proof  of  evolution  considered  as  a  fact,  without 
any  reference  at  all  to  its  method,  let  us  begin  by 
considering  the  antecedent  standing  of  the  matter. 

First  of  all  we  must  clearly  recognise  that  there  are 
only  two  hypotheses  in  the  field  whereby  it  is  possible 
so  much  as  to  suggest  an  explanation  of  the  origin  of 
species.  Either  all  the  species  of  plants  and  animals 
must  have  been  supernaturally  created,  or  else  they 
must  have  been  naturally  evolved.  There  is  no  third 
hypothesis  possible;  for  no  one  can  rationally  suggest 
that  species  have  been  eternal. 

Next,  be  it  observed,  that  the  theory  of  a  continuous 
transmutation  of  species  is  not  logically  bound  to 
furnish  a  full  explanation  of  all  the  natural  causes 
which  it  may  suppose  to  have  been  at  work.  The 
radical  distinction  between  the  two  theories  consists 
in  the  one  assuming  an  immediate  action  of  some 
supernatural  or  inscrutable  cause,  while  the  other 
assumes  the  immediate  action  of  natural — and  there- 
fore of  possibly  discoverable— causes.  But  in  order 
to  sustain  this  latter  assumption,  the  theory  of  descent 
is  under  no  logical  necessity  to  furnish  a  full  proof  of 
all  the  natural  causes  which  may  have  been  concerned 
in  working  out  the  observed  results.  We  do  not 


14  Darwin,  and  after  Darwin. 

know  the  natural  causes  of  many  diseases  ;  but  yet 
no  one  nowadays  thinks  of  reverting  to  any  hypo- 
thesis of  a  supernatural  cause,  in  order  to  explain  the 
occurrence  of  any  disease  the  natural  causation  of 
which  is  obscure.  The  science  of  medicine  being  in 
so  many  cases  able  to  explain  the  occurrence  of 
disease  by  its  hypothesis  of  natural  causes,  medical 
men  now  feel  that  they  are  entitled  to  assume,  on  the 
basis  of  a  wide  analogy,  and  therefore  on  the  basis  of 
a  strong  antecedent  presumption,  that  all  diseases  are 
due  to  natural  causes,  whether  or  not  in  particular 
cases  such  causes  happen  to  have  been  discovered. 
And  from  this  position  it  follows  that  medical  men 
are  not  logically  bound  to  entertain  any  supernatural 
theory  of  an  obscure  disease,  merely  because  as  yet 
they  have  failed  to  find  a  natural  theory.  And  so  it 
is  with  biologists  and  their  theory  of  descent.  Even 
if  it  be  fully  proved  to  them  that  the  causes  which 
they  have  hitherto  discovered,  or  suggested,  are  in- 
adequate to  account  for  all  the  facts  of  organic  nature, 
this  would  in  no  wise  logically  compel  them  to  vacate 
their  theory  of  evolution,  in  favour  of  the  theory  of 
creation.  All  that  it  would  so  compel  them  to  do 
would  be  to  search  with  yet  greater  diligence  for  the 
natural  causes  still  undiscovered,  but  in  the  existence 
of  which  they  are,  by  their  independent  evidence  in 
favour  of  the  theory,  bound  to  believe. 

In  short,  the  issue  is  not  between  the  theory  of  a 
supernatural  cause  and  the  theory  of  any  one  parti- 
cular natural  cause,  or  set  of  causes — such  as  natural 
selection,  use,  disuse,  and  so  forth.  The  issue  thus 
far — or  where  only  the/ar/  of  evolution  is  concerned — 
is  between  the  theory  of  a  supernatural  cause  as 


Introd2ictory.  1 5 

operating  immediately  in  numberless  acts  of  special 
creation,  and  the  theory  of  natural  causes  as  a  whole, 
whether  these  happen,  or  do  not  happen,  to  have  been 
hitherto  discovered. 

This  much  by  way  of  preliminaries  being  under- 
stood, we  have  next  to  notice  that  whichever  of  the 
two  rival  theories  we  choose  to  entertain,  we  are  not 
here  concerned  with  any  question  touching  the  origin 
of  life.  We  are  concerned  only  with  the  origin  of 
particular  forms  of  life — that  is  to  say,  with  the  origin 
of  species.  The  theory  of  descent  starts  from  life  as 
a  datum  already  granted.  How  life  itself  came  to  be, 
the  theory  of  descent,  as  such,  is  not  concerned  to 
show.  Therefore,  in  the  present  discussion,  I  will  take 
the  existence  of  life  as  a  fact  which  does  not  fall 
within  the  range  of  our  present  discussion.  No  doubt 
the  question  as  to  the  origin  of  life  is  in  itself  a  deeply 
interesting  question,  and  although  in  the  opinion  of 
most  biologists  it  is  a  question  which  we  may  well 
hope  will  some  day  fall  within  the  range  of  science  to 
answer,  at  present,  it  must  be  confessed,  science  is  not 
in  a  position  to  furnish  so  much  as  any  suggestion  upon 
the  subject ;  and  therefore  our  wisdom  as  men  of 
science  is  frankly  to  acknowledge  that  such  is  the  case. 

We  are  now  in  a  position  to  observe  that  the  theory 
of  organic  evolution  is  strongly  recommended  to  our 
acceptance  on  merely  antecedent  grounds,  by  the  fact 
that  it  is  in  full  accordance  with  what  is  known  as  the 
principle  of  continuity.  By  the  principle  of  continuity 
is  meant  the  uniformity  of  nature,  in  virtue  of  which 
the  many  and  varied  processes  going  on  in  nature  are 
due  to  the  same  kind  of  method,  i.  e.  the  method  of 


1 6  Darwin,  and  after  Darwin. 

natural  causation.  This  conception  of  the  uniformity 
of  nature  is  one  that  has  only  been  arrived  at  step  by 
step  through  a  long  and  arduous  course  of  human 
experience  in  the  explanation  of  natural  phenomena. 
The  explanations  of  such  phenomena  which  are  first 
given  are  always  of  the  supernatural  kind  ;  it  is  not 
until  investigation  has  revealed  the  natural  causes 
which  are  concerned  that  the  hypotheses  of  super- 
stition give  way  to  those  of  science.  Thus  it  follows 
that  the  hypotheses  of  superstition  which  are  the  latest 
in  yielding  to  the  explanations  of  science,  are  those 
which  refer  to  the  more  recondite  cases  of  natural 
causation  ;  for  here  it  is  that  methodical  investigation 
is  longest  in  discovering  the  natural  causes.  Thus  it 
is  only  by  degrees  that  fetishism  is  superseded  by 
what  now  appears  a  common-sense  interpretation  of 
physical  phenomena;  that  exorcism  gives  place  to 
medicine  ;  alchemy  to  chemistry  ;  astrology  to  astro- 
nomy ;  and  so  forth.  Everywhere  the  miraculous  is 
progressively  banished  from  the  field  of  explanation 
by  the  advance  of  scientific  discovery ;  and  the  places 
where  it  is  left  longest  in  occupation  are  those  where 
the  natural  causes  are  most  intricate  or  obscure,  and 
thus  present  the  greatest  difficulty  to  the  advancing 
explanations  of  science.  Now,  in  our  own  day  there 
are  but  very  few  of  these  strongholds  of  the  mira- 
culous left.  Nearly  the  whole  field  of  explanation  is 
occupied  by  naturalism,  so  that  no  one  ever  thinks  of 
resorting  to  supernaturalism  except  in  the  compara- 
tively few  cases  where  science  has  not  yet  been  able  to 
explore  the  most  obscure  regions  of  causation.  One 
of  these  cases  is  the  origin  of  life  ;  and,  until  quite 
recently,  another  of  these  cases  was  the  origin  of 


Introductory.  \  7 

species.  But  now  that  a  very  reasonable  explanation 
of  the  origin  of  species  has  been  offered  by  science,  it 
is  but  in  accordance  with  all  previous  historical 
analogies  that  many  minds  should  prove  themselves 
unable  all  at  once  to  adjust  themselves  to  the  new 
ideas,  and  thus  still  linger  about  the  more  venerable 
ideas  of  supernaturalism.  But  we  are  now  in  pos- 
session of  so  many  of  these  historical  analogies,  that 
all  minds  with  any  instincts  of  science  in  their 
composition  have  grown  to  distrust,  on  merely  ante- 
cedent grounds,  any  explanation  which  embodies  a 
miraculous  element.  Such  minds  have  grown  to 
regard  all  these  explanations  as  mere  expressions  of 
our  own  ignorance  of  natural  causation ;  or,  in  other 
words,  they  have  come  to  regard  it  as  an  a  priori 
truth  that  nature  is  everywhere  uniform  in  respect  of 
method  or  causation  ;  that  the  reign  of  law  universal ; 
the  principle  of  continuity  ubiquitous. 

Now,  it  must  be  obvious  to  any  mind  which  has 
adopted  this  attitude  of  thought,  that  the  scientific 
theory  of  natural  descent  is  recommended  by  an 
overwhelming  weight  of  antecedent  presumption,  as 
against  the  dogmatic  theory  of  supernatural  design. 

To  begin  with,  we  must  remember  that  the  fact  of 
evolution — or,  which  is  the  same  thing,  the  fact  of 
continuity  in  natural  causation — has  now  been  un- 
questionably proved  in  so  many  other  and  analogous 
departments  of  nature,  that  to  suppose  any  interruption 
of  this  method  as  between  species  and  species  becomes, 
on  grounds  of  such  analogy  alone,  well-nigh  incredible. 
For  example,  it  is  now  a  matter  of  demonstrated  fact 
that  throughout  the  range  of  inorganic  nature  the 
principles  of  evolution  have  obtained.  It  is  no  longer 
*  C 


i8  Darwin,  and  after  Darwin. 

possible  for  any  one  to  believe  with  our  forefathers 
that  the  earth's  surface  has  always  existed  as  it  now 
exists.  For  the  science  of  geology  has  proved  to 
demonstration  that  seas  and  lands  are  perpetually 
undergoing  gradual  changes  of  relative  positions — 
continents  and  oceans  supplanting  each  other  in  the 
course  of  ages,  mountain-chains  being  slowly  uplifted, 
again  as  slowly  denuded,  and  so  forth.  Moreover, 
and  as  a  closer  analogy,  within  the  limits  of  animate 
nature  we  know  it  is  the  universal  law  that  every 
individual  life  undergoes  a  process  of  gradual  develop- 
ment ;  and  that  breeds,  races,  or  strains,  may  be 
brought  into  existence  by  the  intentional  use  of 
natural  processes — the  results  bearing  an  unmistake- 
able  resemblance  to  what  we  know  as  natural  species. 
Again,  even  in  the  case  of  natural  species  themselves, 
there  are  two  considerations  which  present  enormous 
force  from  an  antecedent  point  of  view.  The  first 
is  that  organic  forms  are  only  then  recognised  as 
species  when  intermediate  forms  are  absent.  If  the 
intermediate  forms  are  actually  living,  or  admit  of 
being  found  in  the  fossil  state,  naturalists  forthwith 
regard  the  whole  series  as  varieties,  and  name  all 
the  members  of  it  as  belonging  to  the  same  species. 
Consequently  it  becomes  obvious  that  naturalists,  in 
their  work  of  naming  species,  may  only  have  been 
marking  out  the  cases  where  intermediate  or  con- 
necting forms  have  been  lost  to  observation.  For 
example,  here  we  have  a  diagram  representing  a  very 
unusually  complete  series  of  fossil  shells,  which 
within  the  last  few  years  has  been  unearthed  from 
the  Tertiary  lake  basins  of  Slavonia.  Before  the 
series  was  completed,  some  six  or  eight  of  the  then 


Introductory.  19 

disconnected  forms  were  described  as  distinct  species  ; 
but  as  soon  as  the  connecting  forms  were  found — 
showing  a  progressive  modification  from  the  older  to 
the  newer  beds, — the  whole  were  included  as  varieties 
of  one  species. 


FIG.  i. — Successive  forms  of  Paludina,  from  the  Tertiary  deposits 
of  Slavonia  (after  Neumayr). 

Of  course,  other  cases  of  the  same  kind  might  be 
adduced,  and  therefore,  as  just  remarked,  in  their 
work  of  naming  species  naturalists  may  only  have 


work  ot  naming  species  naturalists  may  only 
been  marking  out  the  cases  where  intermediate 
C  2 


forms 


2O  Darwin,  and  after  Darwin. 

have  been  lost  to  observation.  And  this  possibility 
becomes  little  less  than  a  certainty  when  we  note  the 
next  consideration  which  I  have  to  adduce,  namely, 
that  in  all  their  systematic  divisions  of  plants  and 
animals  in  groups  higher  than  species — such  as  genera, 
families,  orders,  and  the  rest— naturalists  have  at  all 
times  recognised  the  fact  that  the  one  shades  off  into 
the  other  by  such  imperceptible  gradations,  that  it 
is  impossible  to  regard  such  divisions  as  other  than 
conventional.  It  is  important  to  remember  that  this 
fact  was  fully  recognised  before  the  days  of  Darwin. 
In  those  days  the  scientifically  orthodox  doctrine 
was,  that  although  species  were  to  be  regarded  as 
fixed  units,  bearing  the  stamp  of  a  special  creation, 
all  the  higher  taxonomic  divisions  were  to  be  con- 
sidered as  what  may  be  termed  the  artificial  creation 
of  naturalists  themselves.  In  other  words,  it  was 
believed,  and  in  many  cases  known,  that  if  we  could 
go  far  enough  back  in  the  history  of  the  earth,  we 
should  everywhere  find  a  tendency  to  mutual  ap- 
proximation between  allied  groups  of  species  ;  so  that, 
for  instance,  birds  and  reptiles  would  be  found  to  be 
drawing  nearer  and  nearer  together,  until  eventually 
they  would  seem  to  become  fused  in  a  single  type; 
that  the  existing  distinctions  between  herbivorous 
and  carnivorous  mammals  would  be  found  to  do  like- 
wise ;  and  so  on  with  all  the  larger  group-distinctions, 
at  any  rate  within  the  limits  of  the  same  sub-kingdoms. 
But  although  naturalists  recognised  this  even  in  the 
pre-Darwinian  days,  they  stoutly  believed  that  a 
great  exception  was  to  be  made  in  the  case  of  species. 
These,  the  lowest  or  initial  members  of  their  taxo- 
nomic series,  they  supposed  to  be  permanent— the 


Introductory.  2 1 

miraculously  created  units  of  organic  nature.  Now, 
all  that  I  have  at  present  to  remark  is,  that  this 
pre-Darwinian  exception  which  was  made  in  favour 
of  species  to  the  otherwise  recognised  principle  of 
gradual  change,  was  an  exception  which  can  at  no 
time  have  been  recommended  by  any  antecedent 
considerations.  At  all  times  it  stood  out  of  analogy 
with  the  principle  of  continuity  ;  and,  as  we  shall  fully 
find  in  subsequent  chapters,  it  is  now  directly  con- 
tradicted by  all  the  facts  of  biological  science. 

There  remains  one  other  fact  of  high  generality  to 
which  prominent  attention  should  be  drawn  from  the 
present,  or  merely  antecedent,  point  of  view.  On 
the  theory  of  special  creation  no  reason  can  be 
assigned  why  distinct  specific  types  should  present 
any  correlation,  either  in  time  or  in  space,  with  their 
nearest  allies ;  for  there  is  evidently  no  conceivable 
reason  why  any  given  species,  A,  should  have  been 
specially  created  on  the  same  area  and  at  about  the 
same  time  as  its  nearest  representative,  B, — still  less, 
of  course,  that  such  should  be  a  general  rule  through- 
out all  the  thousands  and  millions  of  species  which 
have  ever  inhabited  the  earth.  But,  equally  of  course, 
on  the  theory  of  a  natural  evolution  this  is  so  necessary 
a  consequence,  that  if  no  correlation  of  such  a  two-fold 
kind  were  observable,  the  theory  would  be  negatived. 
Thus  the  question  whether  there  be  any  indication 
of  such  a  two-fold  correlation  may  be  regarded  as 
a  test-question  as  between  the  two  theories ;  for 
although  the  vast  majority  of  extinct  species  have 
been  lost  to  science,  there  are  a  countless  number 
of  existing  species  which  furnish  ample  material  for 
answering  the  question.  And  the  answer  is  so  un- 


22  Darwin,  and  after  Darwin. 

equivocal  that  Mr.  Wallace,  who  is  one  of  our  greatest 
authorities  on  geographical  distribution,  has  laid  it 
down  as  a  general  law,  applicable  to  all  the  depart- 
ments of  organic  nature,  that,  so  far  as  observation 
can  extend,  "  every  species  has  come  into  existence 
coincident  both  in  space  and  time  with  a  pre-existing 
and  closely  allied  species."  As  it  appears  to  me  that 
the  significance  of  these  words  cannot  be  increased  by 
any  comment  upon  them,  I  will  here  bring  this  intro- 
ductory chapter  to  a  close. 


CHAPTER   II. 

CLASSIFICATION. 

THE  first  line  of  direct  evidence  in  favour  of  organic 
evolution  which  I  shall  open  is  that  which  may  be 
termed  the  argument  from  Classification. 

It  is  a  matter  of  observable  fact  that  different  forms 
of  plants  and  animals  present  among  themselves  more 
or  less  pronounced  resemblances.  From  the  earliest 
times,  therefore,  it  has  been  the  aim  of  philosophical 
naturalists  to  classify  plants  and  animals  in  accord- 
ance with  these  resemblances.  Of  course  the  earliest 
attempts  at  such  classification  were  extremely  crude. 
The  oldest  of  these  attempts  with  which  we  are  ac- 
quainted— namely,  that  which  is  presented  in  the  books 
of  Genesis  and  Leviticus — arranges  the  whole  vegetable 
kingdom  in  three  simple  divisions  of  Grass,  Herbs,  and 
Trees  ;  while  the  animal  kingdom  is  arranged  with 
almost  equal  simplicity  with  reference,  first  to  habitats 
in  water,  earth,  or  air,  and  next  as  to  modes  of  pro- 
gression. These,  of  course,  were  what  may  be  termed 
common-sense  classifications,  having  reference  merely 
to  external  appearances  and  habits  of  life.  But  when 
Aristotle  laboriously  investigated  the  comparative 
anatomy  of  animals,  he  could  not  fail  to  perceive  that 
their  entire  structures  had  to  be  taken  into  account  in 


24  Darwin,  and  after  Darwin. 

order  to  classify  them  scientifically  ;  and,  also,  that 
for  this  purpose  the  internal  parts  were  of  quite  as 
much  importance  as  the  external.  Indeed,  he  per- 
ceived that  they  were  of  greatly  more  importance  in 
this  respect,  inasmuch  as  they  presented  so  many 
more  points  for  comparison  ;  and,  in  the  result,  he 
furnished  an  astonishingly  comprehensive,  as  well  as 
an  astonishingly  accurate  classification  of  the  larger 
groups  of  the  animal  kingdom.  On  the  other  hand, 
classification  of  the  vegetable  kingdom  continued 
pretty  much  as  it  had  been  left  by  the  book  of  Genesis 
— all  plants  being  divided  into  three  groups,  Herbs, 
Shrubs,  and  Trees.  Nor  was  this  primitive  state  of 
matters  improved  upon  till  the  sixteenth  century,  when 
Gesner  (1516-1565),  and  still  more  Caesalpino  (1519- 
1603),  laid  the  foundations  of  systematic  botany. 

But  the  more  that  naturalists  prosecuted  their 
studies  on  the  anatomy  of  plants  and  animals,  the 
more  enormously  complex  did  they  find  the  problem 
of  classification  become.  Therefore  they  began  by 
forming  what  are  called  artificial  systems,  in  contra- 
distinction to  natural  systems.  An  artificial  system 
of  classification  is  a  system  based  on  the  more  or  less 
arbitrary  selection  of  some  one  part,  or  set  of  parts ; 
while  a  natural  classification  is  one  that  is  based  upon 
a  complete  knowledge  of  all  the  structures  of  all  the 
organisms  which  are  classified. 

Thus,  the  object  of  classification  has  been  that  of 
arranging  organisms  in  accordance  with  their  natural 
affinities,  by  comparing  organism  with  organism,  for 
the  purpose  of  ascertaining  which  of  the  constituent 
organs  are  of  the  most  invariable  occurrence,  and 
therefore  of  the  most  typical  signification.  A  porpoise, 


Classification.  2  5 

for  instance,  has  a  large  number  of  teeth,  and  in  this 
feature  resembles  most  fish,  while  it  differs  from  all 
mammals.  But  it  also  gives  suck  to  its  young.  Now, 
looking  to  these  two  features  alone,  should  we  say 
that  a  porpoise  ought  to  be  classed  as  a  fish  or  as  a 
mammal?  Assuredly  as  a  mammal  ;  because  the 
number  of  teeth  is  a  very  variable  feature  both  in  fish 
and  mammals,  whereas  the  giving  of  suck  is  an  in- 
variable feature  among  mammals,  and  occurs  nowhere 
else  in  the  animal  kingdom.  This,  of  course,  is  chosen 
as  a  very  simple  illustration.  Were  all  cases  as 
obvious,  there  would  be  but  little  distinction  between 
natural  and  artificial  systems  of  classification.  But  it 
is  because  the  lines  of  natural  affinity  are,  as  it  were, 
so  interwoven  throughout  the  organic  world,  and 
because  there  is,  in  consequence,  so  much  difficulty  in 
following  them,  that  artificial  systems  have  to  be  made 
in  the  first  instance  as  feelers  towards  eventual  dis- 
covery of  the  natural  system.  In  other  words,  while 
forming  their  artificial  systems  of  classification,  it  has 
always  been  the  aim  of  naturalists— whether  con- 
sciously or  unconsciously — to  admit  as  the  bases  of 
their  systems  those  characters  which,  in  the  then  state 
of  their  knowledge,  seemed  most  calculated  to  play  an 
important  part  in  the  eventual  construction  of  the 
natural  system.  If  we  were  dealing  with  the  history 
of  classification,  it  would  here  be  interesting  to  note 
how  the  course  of  it  has  been  marked  by  gradual 
change  in  the  principles  which  naturalists  adopted  as 
guides  to  the  selection  of  characters  on  which  to  found 
their  attempts  at  a  natural  classification.  Some  of 
these  changes,  indeed,  I  shall  have  to  mention  later 
on  ;  but  at  present  what  has  to  be  specially  noted  is, 


26  Darwin,  and  after  Darwin. 

that  through  all  these  changes  of  theory  or  principle, 
and  through  all  the  ever-advancing  construction  of 
their  taxonomic  science,  naturalists  themselves  were 
unable  to  give  any  intelligible  reason  for  the  faith  that 
was  in  them — or  the  faith  that  over  and  above  the 
artificial  classifications  which  were  made  for  the  mere 
purpose  of  cataloguing  the  living  library  of  organic 
nature,  there  was  deeply  hidden  in  nature  itself  a  truly 
natural  classification,  for  the  eventual  discovery  of 
which  artificial  systems  might  prove  to  be  of  more  or 
less  assistance. 

Linnaeus,  for  example,  expressly  says — "You  ask 
me  for  the  characters  of  the  natural  orders  ;  I  confess 
that  I  cannot  give  them."  Yet  he  maintains  that, 
although  he  cannot  define  the  characters,  he  knows, 
by  a  sort  of  naturalist's  instinct,  what  in  a  general  way 
will  subsequently  be  found  to  be  the  organs  of  most 
importance  in  the  eventual  grouping  of  plants  under 
a  natural  system.  "  I  will  not  give  my  reasons  for  the 
distribution  of  the  natural  orders  which  I  have  pub- 
lished," he  said  :  "  you,  or  some  other  person,  after 
twenty  or  after  fifty  years,  will  discover  them,  and  see 
that  I  was  right." 

Thus  we  perceive  that  in  forming  their  provisional 
or  artificial  classifications,  naturalists  have  been  guided 
by  an  instinctive  belief  in  some  general  principle  of 
natural  affinity,  the  character  of  which  they  have  not 
been  able  to  define ;  and  that  the  structures  which 
they  selected  as  the  bases  of  their  classifications  when 
these  were  consciously  artificial,  were  selected  because 
it  seemed  that  they  were  the  structures  most  likely  to 
prove  of  use  in  subsequent  attempts  at  working  out  the 
natural  system. 


Classification.  2  7 

This  general  principle  of  natural  affinity,  of  which 
all  naturalists  have  seen  more  or  less  well-marked 
evidence  in  organic  nature,  and  after  which  they  have 
all  been  feeling,  has  sometimes  been  regarded  as 
natural,  but  more  often  as  supernatural.  Those  who 
regarded  it  as  supernatural  took  it  to  consist  in  a 
divine  ideal  of  creation  according  to  types,  so  that  the 
structural  affinities  of  organisms  were  to  them  expres- 
sions of  an  archetypal  plan,  which  might  be  revealed 
in  its  entirety  when  all  organisms  on  the  face  of  the 
earth  should  have  been  examined.  Those,  on  the 
other  hand,  who  regarded  the  general  principle  of 
affinity  as  depending  on  some  natural  causes,  for  the 
most  part  concluded  that  these  must  have  been  utili- 
tarian causes  ;  or,  in  other  words,  that  the  fundamental 
affinities  of  structure  must  have  depended  upon  funda- 
mental requirements  of  function.  According  to  this 
view,  the  natural  classification  would  eventually  be 
found  to  stand  upon  a  basis  of  physiology.  Therefore 
all  the  systems  of  classification  up  to  the  earlier  part 
of  the  present  century  went  upon  the  apparent  axiom, 
that  characters  which  are  of  most  importance  to  the 
organisms  presenting  them  must  be  characters  most 
indicative  of  natural  affinities.  But  the  truth  of  the 
matter  was  eventually  found  to  be  otherwise.  For  it 
was  eventually  found  that  there  is  absolutely  no  cor- 
relation between  these  two  things ;  that,  therefore,  it 
is  a  mere  chance  whether  or  not  organs  which  are  of 
importance  to  organisms  are  likewise  of  importance  as 
guides  to  classification  ;  and,  in  point  of  fact,  that  the 
general  tendency  in  this  matter  is  towards  an  inverse 
instead  of  a  direct  proportion.  More  often  than  not, 
the  greater  the  value  of  a  structure  for  the  purpose  of 


28  Darwin,  and  after  Darwin. 

indicating  natural  affinities,  the  less  is  its  value  to  the 
creatures  presenting  it. 

Enough  has  now  been  said  to  show  three  things. 
First;  that  long  before  the  theory  of  descent  was  enter- 
tained by  naturalists,  naturalists  perceived  the  fact  of 
natural  affinities,  and  did  their  best  to  construct  a 
natural  system  of  classification  for  the  purpose  of  ex- 
pressing such  affinities.  Second,  that  naturalists  had 
a  kind  of  instinctive  belief  in  some  one  principle  run- 
ning through  the  whole  organic  world,  which  thus 
served  to  bind  together  organisms  in  groups  subor- 
dinate to  groups — that  is,  into  species,  genera,  orders, 
families,  classes,  sub-kingdoms,  and  kingdoms.  Third, 
that  they  were  not  able  to  give  any  very  intelligible 
reason  for  this  faith  that  was  in  them  ;  sometimes 
supposing  the  principle  in  question  to  be  that  of  a 
supernatural  plan  of  organization,  sometimes  regarding 
it  as  dependent  on  conditions  of  physiology,  and  some- 
times not  attempting  to  account  for  it  at  all. 

Of  course  it  is  obvious  that  the  theory  of  descent 
furnishes  the  explanation  which  is  required.  For  it  is 
now  evident  to  evolutionists,  that  although  these  older 
naturalists  did  not  know  what  they  were  doing  when 
they  were  tracing  these  lines  of  natural  affinity,  and 
thus  helping  to  construct  a  natural  classification — I  say 
it  is  now  evident  to  evolutionists  that  these  naturalists 
were  simply  tracing  the  lines  of  genetic  relationship. 
The  great  principle  pervading  organic  nature,  which 
was  seen  so  mysteriously  to  bind  the  whole  creation 
together  as  in  a  nexus  of  organic  affinity,  is  now  easily 
understood  as  nothing  more  CH.  less  than  the  prin- 
ciple of  Heredity.  Let  us,  therefore,  look  a  little 
more  closely  at  the  character  df  this  network,  in 


Classification.  29 

order  to  see  how  far  it  lends  itself  to  this  new  inter- 
pretaticn. 

The  first  thing  that  we  have  to  observe  about  the 
nexus  is,  that  it  is  a  nexus — not  a  single  line,  or  even 
a  series  of  parallel  lines.  In  other  words,  some  time 
before  the  theory  of  descent  was  seriously  entertained, 
naturalists  for  the  most  part  had  fully  recognised  that 
it  was  impossible  to  arrange  either  plants  or  animals, 
with  respect  to  their  mutual  affinities,  in  a  ladder-like 
series  (as  was  supposed  to  be  the  type  of  classification 
by  the  earlier  systematists),  or  even  in  map-like  groups 
(as  was  supposed  to  be  the  type  by  Linnaeus).  And 
similarly,  also,  with  respect  to  grades  of  organization. 
In  the  case  of  the  larger  groups,  indeed,  it  is  usually 
possible  to  say  that  the  members  of  this  group  as  a 
whole  are  more  highly  organized  than  the  members  of 
that  group  as  a  whole ;  so  that,  for  instance,  we  have 
no  hesitation  in  regarding  the  Vertebrata  as  more 
highly  organized  than  the  Invertebrata,  Birds  than 
Reptiles,  and  so  on.  But  when  we  proceed  to  smaller 
subdivisions,  such  as  genera  and  species,  it  is  usually 
impossible  to  say  that  the  one  type  is  more  highly 
organized  than  another  type.  A  horse,  for  instance, 
cannot  be  said  to  be  more  highly  organized  than  a 
zebra  or  an  ass ;  although  the  entire  horse-genus  is 
clearly  a  more  highly  organized  type  than  any  genus 
of  animal  which  is  not  a  mammal. 

In  view  of  these  facts,  therefore,  the  system  of 
classification  which  was  eventually  arrived  at  before 
the  days  of  Darwin,  was  the  system  which  naturalists 
likened  to  a  tree ;  and  this  is  the  system  which  all 
naturalists  now  agreed  upon  as  the  true  one.  Ac- 
cording to  this  system,  a  short  trunk  may  be  taken 


30  Darwin,  and  after  Darwin. 

to  represent  the  lowest  organisms  which  cannot 
properly  be  termed  either  plants  or  animals.  This 
short  trunk  soon  separates  into  two  large  trunks,  one 
of  which  represents  the  vegetable  and  the  other  the 
animal  kingdom.  Each  of  these  trunks  then  gives  off 
large  branches  signifying  classes,  and  these  give  off 
smaller,  but  more  numerous  branches,  signifying 
families,  which  ramify  again  into  orders,  genera,  and 
finally  into  the  leaves,  which  may  be  taken  to  repre- 
sent species.  Now,  in  such  a  representative  tree  of 
life,  the  height  of  any  branch  from  the  ground  may  be 
taken  to  indicate  the  grade  of  organization  which  the 
leaves,  or  species,  present ;  so  that,  if  we  picture  to 
ourselves  such  a  tree,  we  may  understand  that  while 
there  is  a  general  advance  of  organization  from  below 
upwards,  there  are  many  deviations  in  this  respect. 
Sometimes  leaves  growing  on  the  same  branch  are 
growing  at  a  different  level — especially,  of  course,  if 
the  branch  be  a  large  one,  corresponding  to  a  class  or 
sub-kingdom.  And  sometimes  leaves  growing  on 
different  branches  are  growing  at  the  same  level : 
that  is  to  say,  although  they  represent  species  be- 
longing to  widely  divergent  families,  orders,  or  even 
classes,  it  cannot  be  said  that  the  one  species  is  more 
highly  organized  than  the  other. 

Now,  this  tree-like  arrangement  of  species  in  nature 
is  an  arrangement  for  which  Darwin  is  not  responsible. 
For,  as  we  have  seen,  the  detecting  of  it  has  been 
due  to  the  progressive  work  of  naturalists  for  centuries 
past ;  and  even  when  it  was  detected,  at  about  the 
commencement  of  the  present  century,  naturalists 
were  confessedly  unable  to  explain  the  reason  of  it, 
or  what  was  the  underlying  principle  that  they  were 


Classification.  3 1 

engaged  in  tracing  when  they  proceeded  ever  more 
and  more  accurately  to  define  these  ramifications  of 
natural  affinity.  But  now,  as  just  remarked,  we  can 
clearly  perceive  that  this  underlying  principle  was  none 
other  than  Heredity  as  expressed  in  family  likeness, 
— likeness,  therefore,  growing  progressively  more 
unlike  with  remoteness  of  ancestral  relationship.  For 
thus  only  can  we  obtain  any  explanation  of  the  sundry 
puzzles  and  apparent  paradoxes,  which  a  working  out 
of  their  natural  classifications  revealed  to  botanists  and 
zoologists  during  the  first  half  of  the  present  century. 
It  will  now  be  my  endeavour  to  show  how  these 
puzzles  and  paradoxes  are  all  explained  by  the  theory 
that  natural  affinities  are  merely  the  expression  of 
genetic  affinities. 

First  of  all,  and  from  the  most  general  point  of 
view,  it  is  obvious  that  the  tree-like  system  of  classifi- 
cation, which  Darwin  found  already  and  empirically 
worked  out  by  the  labours  of  his  predecessors,  is  as 
suggestive  as  anything  could  well  be  of  the  fact  of 
genetic  relationship.  For  this  is  the  form  that  every 
tabulation  of  family  pedigree  must  assume  ;  and  there- 
fore the  mere  fact  that  a  scientific  tabulation  of  natural 
affinities  was  eventually  found  to  take  the  form  of  a 
tree,  is  in  itself  highly  suggestive  of  the  inference  that 
such  a  tabulation  represents  a  family  tree.  If  all 
species  were  separately  created,  there  can  be  no  assign- 
able reason  why  the  ideas  of  earlier  naturalists  touch- 
ing the  form  which  a  natural  classification  would 
eventually  assume  should  not  have  represented  the 
truth — why,  for  example,  it  should  not  have  assumed 
the  form  of  a  ladder  (as  was  anticipated  in  the 
seventeenth  century),  or  of  a  map  (as  was  anticipated  in 


32  Darwin,  and  after  Darwin. 

the  eighteenth),  or,  again,  of  a  number  of  wholly  unre- 
lated lines,  circles,  &c.  (as  certain  speculative  writers  of 
the  present  century  have  imagined).  But,  on  the  other 
hand,  if  all  species  were  separately  and  independently 
created,  it  becomes  virtually  incredible  that  we  should 
everywhere  observe  this  progressive  arborescence  of 
characters  common  to  larger  groups  into  more  and 
more  numerous,  and  more  and  more  delicate,  ramifi- 
cations of  characters  distinctive  only  of  smaller  and 
smaller  groups.  A  man  would  be  deemed  insane  if  he 
were  to  attribute  the  origin  of  every  branch  and  every 
twig  of  a  real  tree  to  a  separate  act  of  special  creation  ; 
and  although  we  have  not  been  able  to  witness  the 
growth  of  what  we  may  term  in  a  new  sense  the  Tree 
of  Life,  the  structural  relations  which  are  now  apparent 
between  its  innumerable  ramifications  bear  quite  as 
strong  a  testimony  to  the  fact  of  their  having  been 
due  to  an  organic  growth,  as  is  the  testimony  furnished 
by  the  branches  of  an  actual  tree. 

Or,  to  take  another  illustration.  Classification  of 
organic  forms,  as  Darwin,  Lyell,  and  Hackel  have 
pointed  out,  strongly  resembles  the  classification  of 
languages.  In  the  case  of  languages,  as  in  the  case 
of  species,  we  have  genetic  affinities  strongly  marked  ; 
so  that  it  is  possible  to  some  extent  to  construct  a 
Language-tree,  the  branches  of  which  shall  indicate, 
in  a  diagrammatic  form,  the  progressive  divergence  of  a 
large  group  of  languages  from  a  common  stock.  For 
instance,  Latin  may  be  regarded  as  a  fossil  language, 
which  has  given  rise  to  a  group  of  living  languages — 
Italian,  Spanish,  French,  and,  to  a  large  extent, 
English.  Now  what  would  be  thought  of  a  philologist 
who  should  maintain  that  English,  French,  Spanish, 


Classification.  33 

and  Italian  were  all  specially  created  languages — or 
languages  separately  constructed  by  the  Deity,  and 
by  as  many  separate  acts  of  inspiration  communicated 
to  the  nations  which  now  speak  them  — and  that  their 
resemblance  to  the  fossil  form,  Latin,  must  be 
attributed  to  special  design  ?  Yet  the  evidence  of  the 
natural  transmutation  of  species  is  in  one  respect 
much  stronger  than  that  of  the  natural  transmutation 
of  languages — in  respect,  namely,  of  there  being  a 
vastly  greater  number  of  cases  all  bearing  testimony 
to  the  fact  of  genetic  relationship. 

But,  quitting  now  this  most  general  point  of  view — 
or  the  suggestive  fact  that  what  we  have  before  us  is 
a  tree—  let  us  next  approach  this  tree  for  the  purpose 
of  examining  its  structure  more  in  detail.  When  we 
do  this,  the  fact  of  next  greatest  generality  which  we 
find  is  as  follows. 

In  cases  where  a  very  old  form  of  life  has  continued 
to  exist  unmodified,  so  that  by  investigation  of  its 
anatomy  we  are  brought  back  to  a  more  primitive 
type  of  structure  than  that  of  the  newer  forms  grow- 
ing higher  up  ttpon  the  same  branch^  two  things  are 
observable.  In  the  first  place,  the  old  form  is  less 
differentiated  than  the  newer  ones  ;  and,  in  the  next 
place,  it  is  seen  much  more  closely  to  resemble  types 
of  structure  belonging  to  some  of  the  other  and  larger 
branches  of  the  tree.  The  organization  of  the  older 
form  is  not  only  simpler  ;  but  it  is,  as  naturalists  say, 
more  generalized.  It  comprises  within  itself  char- 
acters belonging  to  its  own  branch,  and  also  characters 
belonging  to  neighbouring  branches,  or  to  the  trunk 
from  which  allied  branches  spring.  Hence  it  becomes 
a  general  rule  of  classification,  that  it  is  by  the  lowest, 
*  D 


34  Darwin,  and  after  Darwin. 

or  by  the  oldest,  forms  of  any  two  natural  groups  that 
the  affinities  between  the  two  groups  admit  of  being 
best  detected.  And  it  is  obvious  that  this  is  just 
what  ought  to  be  the  case  on  the'  theory  of  descent 
with  divergent  modification  ;  while,  upon  the  alter- 
native theory  of  special  creation,  no  reason  can  be 
assigned  why  the  lowest  or  the  oldest  types  should 
thus  combine  the  characters  which  afterwards  become 
severally  distinctive  of  higher  or  newer  types. 

Again,  I  have  already  alluded  to  the  remarkable 
fact  that  there  is  no  correlation  between  the  value  of 
structures  to  the  organisms  which  present  them,  and 
their  value  to  the  naturalist  for  the  purpose  of  tracing 
natural  affinity ;  and  I  have  remarked  that  up  to  the 
close  of  the  last  century  it  was  regarded  as  an  axiom 
of  taxonomic  science,  that  structures  which  are  of 
most  importance  to  the  animals  or  plants  possessing 
them  must  likewise  prove  of  most  importance  in  any 
natural  system  of  classification.  On  this  account,  all 
attempts  to  discover  the  natural  classification  went 
upon  the  supposition  that  such  a  direct  proportion 
must  obtain — with  the  result  that  organs  of  most 
physiological  importance  were  chosen  as  the  bases  of 
systematic  work.  And  when,  in  the  earlier  part  of 
the  present  century,  De  Candolle  found  that  instead 
of  a  direct  there  was  usually  an  inverse  proportion 
between  the  functional  and  the  taxonomic  value  of  a 
structure,  he  was  unable  to  suggest  any  reason  for 
this  apparently  paradoxical  fact.  For,  upon  the 
theory  of  special  creation,  no  reason  can  be  assigned 
why  organs  of  least  importance  to  organisms  should 
prove  of  most  importance  as  marks  of  natural  affinity. 
But  on  the  theory  of  descent  with  progressive  modi- 


Classification.  35 

fication  the  apparent  paradox  is  at  once  explained. 
For  it  is  evident  that  organs  of  functional  importance 
are,  other  things  equal,  the  organs  which  are  most 
likely  to  undergo  different  modifications  in  different 
lines  of  family  descent,  and  therefore  in  time  to  have 
their  genetic  relationships  in  these  different  lines 
obscured.  On  the  other  hand,  organs  or  structures 
which  are  of  no  functional  importance  are  never  called 
upon  to  change  in  response  to  any  change  of  habit,  or 
to  any  change  in  the  conditions  of  life.  They  may, 
therefore,  continue  to  be  inherited  through  many 
different  lines  of  family  descent,  and  thus  afford 
evidence  of  genetic  relationship  where  such  evidence 
fails  to  be  given  by  any  of  the  structures  of  vital 
importance,  which  in  the  course  of  many  generations 
have  been  required  to  change  in  many  ways  according 
to  the  varied  experiences  of  different  branches  of  the 
same  family.  Here,  then,  we  have  an  empirically 
discovered  rule  in  the  science  of  classification,  the 
raison  d'etre  of  which  we  are  at  once  able  to  appre- 
ciate upon  the  theory  of  evolution,  whereas  no 
possible  explanation  of  why  it  should  ever  have 
become  a  rule  could  be  furnished  upon  the  theory  of 
special  creation. 

Here,  again,  is  another  empirically  determined  rule. 
The  larger  the  number,  as  distinguished  from  the 
importance,  of  structures  which  are  found  common 
to  different  groups,  the  greater  becomes  their  value 
as  guides  to  the  determination  of  natural  affinity. 
Or,  as  Darwin  puts  it,  "  the  value  of  an  aggre- 
gate of  characters,  even  when  none  are  important, 
alone  explains  the  aphorism  enunciated  by  Linnaeus, 
namely,  that  the  characters  do  not  give  the  genus, 
D  2 


36  Darwin,  and  after  Darwin. 

but  the  genus  gives  the  characters;  for  this  seems 
founded  on  the  appreciation  of  many  trifling  points 
of  resemblance,  too  slight  to  be  defined 1." 

Now  it  is  evident,  without  comment,  of  how  much 
value  aggregates  of  characters  ought  to  be  in  classifica- 
tion, if  the  ultimate  meaning  of  classification  be  that 
of  tracing  lines  of  pedigree  ;  whereas,  if  this  ultimate 
meaning  were  that  of  tracing  divine  ideals  manifested 
in  special  creation,  we  can  see  no  reason  why  single 
characters  are  not  .such  sure  tokens  of  a  natural 
arrangement  as  are  aggregates  of  characters,  even 
though  the  latter  be  in  every  other  respect  unim- 
portant. For,  on  the  special  creation  theory,  we 
cannot  explain  why  an  assemblage,  say  of  four  or 
five  trifling  characters,  should  have  been  chosen  to 
mark  some  unity  of  plan,  rather  than  some  one 
character  of  functional  importance,  which  would  have 
served  at  least  equally  well  any  such  hypothetical 
purpose.  On  the  other  hand,  as  Darwin  remarks,  "  we 
care  not  how  trifling  a  character  may  be — let  it  be  the 
mere  inflection  of  the  angle  of  the  jaw,  the  manner  in 
which  an  insect's  wing  is  folded,  whether  the  skin  be 
covered  with  hair  or  feathers — if  it  prevail  throughout 
many  and  different  species,  especially  those  having 
very  different  habits  of  life,  it  assumes  high  value; 
for  we  can  account  for  its  presence  in  so  many  forms, 
with  such  different  habits,  only  by  inheritance  from  a 
common  parent.  We  may  err  in  this  respect  in  regard 
to  single  points  of  structure,  but  when  several  char- 
acters, let  them  be  ever  so  trifling,  concur  throughout 
a  large  group  of  beings  having  different  habits,  we 
may  feel  almost  sure,  on  the  theory  of  descent; 

1  Origin  of  Species,  p.  367. 


Classification.  37 

that  these  characters  have  been  inherited  from  a 
common  ancestor  ;  and  we  know  that  such  aggregated 
characters  have  especial  value  in  classification  V 

It  is  true  that  even  a  single  character,  if  found 
common  to  a  large  number  of  forms,  while  uniformly 
absent  from  others,  is  also  regarded  by  naturalists  as 
of  importance  for  purposes  of  classification,  although 
they  recognise  it  as  of  a  value  subordinate  to  that  of 
aggregates  of  characters.  But  this  also  is  what  we 
should  expect  on  the  theory  of  descent.  If  even  any 
one  structure  be  found  to  run  through  a  number  of 
animals  presenting  different  habits  of  life,  the  readiest 
explanation  of  the  fact  is  to  be  found  in  the  theory  of 
descent ;  but  this  does  not  hinder  that  if  several  such 
characters  always  occur  together,  the  inference  of 
genetic  relationship  is  correspondingly  confirmed. 
And  the  fact  that  before  this  inference  was  ever  drawn, 
naturalists  recognised  the  value  of  single  characters  in 
proportion  to  their  constancy,  and  the  yet  higher 
value  of  aggregates  of  characters  in  proportion  to 
their  number — this  fact  shows  that  in  their  work  of 
classification  naturalists  empirically  observed  the 
effects  of  a  cause  which  we  have  now  discovered,  to 
wit,  hereditary  transmission  of  characters  through 
ever- widening  groups  of  changing  species. 

There  is  another  argument  which  appears  to  tell 
strongly  in  favour  of  the  theory  of  descent.  We  have 
just  seen  that  non-adaptive  structures,  not  being 
required  to  change  in  response  to  change  of  habits  or 
conditions  of  life,  are  allowed  to  persist  unchanged 
through  many  generations,  and  thus  furnish  excep- 
tionally good  guides  in  the  science  of  classification — 

1  Origin  of  Species,  p.  372. 


38  Darwin,  and  after  Darwin. 

or,  according  to  our  theory,  in  the  work  of  tracing 
lines  of  pedigree.  But  now,  the  converse  of  this 
statement  holds  equally  true.  For  it  often  happens 
that  adaptive  structures  are  required  to  change  in 
different  lines  of  descent  in  analogous  ways,  in  order 
to  meet  analogous  needs  ;  and,  when  such  is  the  case, 
the  structures  concerned  have  to  assume  more  or 
less  close  resemblances  to  one  another,  even  though 
they  have  severally  descended  from  quite  different 
ancestors.  The  paddles  of  a  whale,  for  instance,  most 
strikingly  resemble  the  fins  of  a  fish  as  to  their  out- 
ward form  and  movements ;  yet,  on  the  theory  of 
descent,  they  must  be  held  to  have  had  a  widely 
different  parentage.  Now,  in  all  such  cases  where 
there  is  thus  what  is  called  an  analogous  (or  adaptive) 
resemblance,  as  distinguished  from  what  is  called  an 
homologous  (or  anatomical)  resemblance — in  all  such 
cases  it  is  observable  that  the  similarities  do  not 
extend  further  into  the  structure  of  the  parts  than  it 
is  necessary  that  they  should  extend,  in  order  that  the 
structures  should  both  perform  the  same  functions. 
The  whole  anatomy  of  the  paddles  of  a  whale  is  quite 
unlike  that  of  the  fins  of  a  fish— being,  in  fact,  that  of 
the  fore-limb  of  a  mammal.  The  change,  therefore, 
which  the  fore-limb  has  here  undergone  to  suit  it  to 
the  aquatic  habits  of  this  mammal,  is  no  greater  than 
was  required  for  that  purpose:  the  change  has  not 
extended  to  any  one  feature  of  anatomical  significance. 
This,  of  course,  is  what  we  should  expect  on  the 
theory  of  descent  with  modification  of  ancestral  char- 
acters ;  but  on  the  theory  of  special  creation  it  is  not 
intelligible  why  there  should  always  be  so  marked  a 
distinction  between  resemblances  as  analogical  or 


Classification.  39 

adaptive,  and  resemblances  as  homological  or  of 
meaning  in  reference  to  a  natural  classification.  To 
take  another  and  more  detailed  instance,  the  Tas- 
manian  wolf  is  an  animal  separated  from  true  wolves 
in  a  natural  system  of  classification.  Yet  its  jaws  and 
teeth  bear  a  strong  general  resemblance  to  those  of 
all  the  dog  tribe,  although  there  are  differences  of 
anatomical  detail.  In  particular,  while  the  dogs  all 
have  on  each  side  of  the  upper  jaw  four  pre-molars 
and  two  molars,  the  Tasmanian  wolf  has  three  pre- 
molars  and  four  molars.  Now  there  is  no  reason,  so 
far  as  their  common  function  of  dealing  with  flesh  is 
concerned,  why  the  teeth  of  the  Tasmanian  wolf 
should  not  have  resembled  homologically  as  well  as 
analogically  the  teeth  of  a  true  wolf;  and  therefore 
we  cannot  assign  any  intelligible  reason  why,  if  all  the 
species  of  the  dog  genus  were  separately  created  with 
one  pattern  of  teeth,  the  unallied  Tasmanian  wolf 
should  have  been  furnished  with  what  is  practically 
the  same  pattern  from  a  functional  point  of  view, 
while  differing  from  a  structural  point  of  view.  But, 
of  course,  on  the  theory  of  descent  with  modifica- 
tion, we  can  well  understand  why  similarities  of 
habit  should  have  led  to  similarities  of  structural 
appearance  of  an  adaptive  kind  in  different  lines  of 
descent,  without  there  being  any  trace  of  such  real  or 
anatomical  similarities  as  could  possibly  point  to 
genetic  relationship. 

Lastly,  to  adduce  the  only  remaining  argument 
from  classification  which  I  regard  as  of  any  consider- 
able weight,  naturalists  have  found  it  necessary,  while 
constructing  their  natural  classifications,  to  set  great 
store  on  what  Mr.  Darwin  calls  "  chains  of  affinities." 


4O  Darwin,  and  after  Darwin. 

Thus,  for  instance,  "  nothing  can  be  easier  than  to 
define  a  number  of  characters  common  to  all  birds; 
but  with  crustaceans  any  such  definition  has  hitherto 
been  found  impossible.  There  are  crustaceans  at  the 
opposite  ends  of  the  series,  which  have  hardly  a 
character  in  common  ;  yet  the  species  at  both  ends, 
from  being  plainly  allied  to  others,  and  these  to  others, 
and  so  onwards,  can  be  recognised  as  unequivocally 
belonging  to  this,  and  to  no  other  class  of  the  arti- 
culata  V  Now  it  is  evident  that  this  progressive 
modification  of  specific  types — where  it  cannot  be 
said  that  the  continuity  of  resemblance  is  anywhere 
broken,  and  yet  terminates  in  modification  so  great 
that  but  for  the  connecting  links  no  one  could  divine 
a  natural  relationship  between  the  extreme  members 
of  the  series, — it  is  evident  that  such  chains  of  af- 
finity speak  most  strongly  in  favour  of  a  transmutation 
of  the  species  concerned,  while  it  is  impossible  to 
suggest  any  explanation  of  the  fact  in  terms  of  the 
rival  theory.  For  if  all  the  links  of  such  a  chain 
were  separately  forged  by  as  many  acts  of  special 
creation,  we  can  see  no  reason  why  B  should  re- 
semble A,  C  resemble  B,  and  so  on,  but  with  ever 
slight  though  accumulating  differences,  until  there  is 
no  resemblance  at  all  between  A  and  Z. 

I  hope  enough  has  now  been  said  to  show  that  all 
the  general  principles  and  particular  facts  appertaining 
to  the  natural  classification  of  plants  and  animals,  are 
precisely  what  they  ought  to  be  according  to  the 
theory  of  genetic  descent ;  while  no  one  of  them  is 
such  as  might  be— and,  indeed,  used  to  be — expected 

1  Origin  of  Species,  pp.  368  9. 


Classification.  4 1 

upon  the  theory  of  special  creation.  Therefore,  the 
only  possible  way  in  which  all  this  uniform  body  of 
direct  evidence  can  be  met  by  a  supporter  of  the 
latter  theory,  is  by  falling  back  upon  the  argument 
from  ignorance.  We  do  not  know,  it  may  be  said, 
what  hidden  reasons  there  may  have  been  for  fol- 
lowing all  these  general  principles  in  the  separate 
creation  of  specific  types.  Now,  it  is  evident  that 
this  is  a  form  of  argument  which  admits  of  being 
brought  against  all  the  actual — and  even  all  the 
possible — lines  of  evidence  in  favour  of  evolution. 
Therefore  I  deem  it  desirable  thus  early  in  our  pro- 
ceedings to  place  this  argument  from  ignorance  on  its 
proper  logical  footing. 

If  there  were  any  independent  evidence  in  favour  of 
special  creation  as  a  fact,  then  indeed  the  argument 
from  ignorance  might  be  fairly  used  against  any  sceptical 
cavils  regarding  the  method.  In  this  way,  for  example, 
Bishop  Butler  made  a  legitimate  use  of  the  argument 
from  ignorance  when  he  urged  that  it  is  no  reasonable 
objection  against  a  revelation,  otherwise  accredited,  to 
show  that  it  has  been  rendered  in  a  form,  or  after  a 
method,  which  we  should  not  have  antecedently  ex- 
pected. But  he  could  not  have  legitimately  employed 
this  argument,  except  on  the  supposition  that  he  had 
some  independent  evidence  in  favour  of  the  revela- 
tion ;  for,  in  the  absence  of  any  such  independent 
evidence,  appeal  to  the  argument  from  ignorance 
would  have  become  a  mere  begging  of  the  question, 
by  simply  assuming  that  a  revelation  had  been  made. 
And  thus  it  is  in  the  present  case.  A  man,  of  course, 
may  quite  legitimately  say,  Assuming  tJiat  the  theory  of 
special  creation  is  true,  it  is  not  for  us  to  anticipate  the 


42  Darwin,  and  after  Darwin. 

form  or  method  of  the  process.  But  where  the  question 
is  as  to  whether  or  not  the  theory  is  true,  it  becomes 
a  mere  begging  of  this  question  to  take  refuge  in  the 
argument  from  ignorance,  or  to  represent  in  effect 
that  there  is  no  question  to  be  discussed.  And  if, 
when  the  form  or  method  is  investigated,  it  be  found 
everywhere  charged  with  evidence  in  favour  of  the 
theory  of  descent,  the  case  becomes  the  same  as  that 
of  a  supposed  revelation,  which  has  been  discredited 
by  finding  that  all  available  evidence  points  to  a 
natural  growth.  In  short,  the  argument  from  ignor- 
ance is  in  any  case  available  only  as  a  negative  foil 
against  destructive  criticism  :  in  no  case  has  it  any 
positive  value,  or  value  of  a  constructive  kind.  There- 
fore, if  a  theory  on  any  subject  is  destitute  of  positive 
evidence,  while  some  alternative  theory  is  in  possession 
of  such  evidence,  the  argument  from  ignorance  can  be 
of  no  logical  use  to  the  former,  even  though  it  may  be 
of  such  use  to  the  latter.  For  it  is  only  the  possession 
of  positive  evidence  which  can  furnish  a  logical  justifi- 
cation of  the  argument  from  ignorance  :  in  the  absence 
of  such  evidence,  even  the  negative  value  of  the  argu- 
ment disappears,  and  it  then  implies  nothing  more 
than  the  gratuitous  assumption  of  a  theory. 

I  will  now  sum  up  the  various  considerations  which 
have  occupied  us  during  the  present  chapter. 

First  of  all  we  must  take  note  that  the  classification 
of  plants  and  animals  in  groups  subordinate  to  groups 
is  not  merely  arbitrary,  or  undertaken  only  for  a 
matter  of  convenience  and  nomenclature — such,  for 
instance,  as  the  classification  of  stars  in  constellations. 
On  the  contrary,  the  classification  of  a  naturalist 


Classification.  43 

differs  from  that  of  an  astronomer,  in  that  the 
objects  which  he  has  to  classify  present  structural 
resemblances  and  structural  differences  in  numberless 
degrees ;  and  it  is  the  object  of  his  classification  to 
present  a  tabular  statement  of  these  facts.  Now, 
long  before  the  theory  of  evolution  was  entertained, 
naturalists  became  fully  aware  that  these  facts  of 
structural  resemblances  running  through  groups  sub- 
ordinate to  groups  were  really  facts  of  nature,  and 
not  merely  poetic  imaginations  of  the  mind.  No  one 
could  dissect  a  number  of  fishes  without  perceiving 
that  they  were  all  constructed  on  one  anatomical 
pattern,  which  differed  considerably  from  the  equally 
uniform  pattern  on  which  all  mammals  were  con- 
structed, even  although  some  mammals  bore  an 
extraordinary  resemblance  to  fish  in  external  form 
and  habits  of  life.  And  similarly  with  all  the  smaller 
divisions  of  the  animal  and  vegetable  kingdoms. 
Everywhere  investigation  revealed  the  bonds  of  close 
structural  resemblances  between  species  of  the  same 
genus,  resemblance  less  close  between  genera  of  the 
same  family,  resemblance  still  less  close  between 
families  of  the  same  order,  resemblance  yet  more 
remote  between  orders  of  the  same  class,  and  resem- 
blance only  in  fundamental  features  between  classes 
of  the  same  sub-kingdom,  beyond  which  limit  all 
anatomical  resemblance  was  found  to  disappear — 
the  different  sub-kingdoms  being  formed  on  wholly 
different  patterns.  Furthermore,  in  tracing  all  these 
grades  of  structural  relationship,  naturalists  were 
slowly  led  to  recognise  that  the  form  which  a  natural 
classification  must  eventually  assume  would  be  that 
of  a  tree,  wherein  the  constituent  branches  would 


44  Darwin,  and  after  Darwin. 

display  a  progressive  advance  of  organization  from 
below  upwards. 

Now  we  have  seen  that  although  this  tree-like 
arrangement  of  natural  groups  was  as  suggestive  as 
anything  could  well  be  of  all  the  forms  of  life  being 
bound  together  by  the  ties  of  genetic  relationship, 
such  was  not  the  inference  which  was  drawn  from  it. 
Dominated  by  the  theory  of  special  creation,  natu- 
ralists either  regarded  the  resemblance  of  type  subor- 
dinate to  type  as  expressive  of  divine  ideals  mani- 
fested in  such  creation,  or  else  contented  themselves 
with  investigating  the  facts  without  venturing  to 
speculate  upon  their  philosophical  import.  But  even 
those  naturalists  who  abstained  from  committing 
themselves  to  any  theory  of  archetypal  plans,  did 
not  doubt  that  facts  so  innumerable  and  so  uni- 
versal must  have  been  due  to  some  one  co-ordi- 
nating principle — that,  even  though  they  were  not 
able  to  suggest  what  it  was.  there  must  have  been 
some  hidden  bond  of  connexion  running  through  the 
whole  of  organic  nature.  Now,  as  we  have  seen,  it  is 
manifest  to  evolutionists  that  this  hidden  bond  can  be 
nothing  else  than  heredity  ;  and,  therefore,  that  these 
earlier  naturalists,  although  they  did  not  know  what 
they  were  doing,  were  really  tracing  the  lines  of 
genetic  descent  as  revealed  by  degrees  of  structural 
resemblance,— that  the  arborcsent  grouping  of  organic 
forms  which  their  labours  led  them  to  begin,  and  in 
large  measure  to  execute,  was  in  fact  a  family  tree  of 
life. 

Here,  then,  is  the  substance  of  the  argument  from 
classification.  The  mere  fact  that  all  organic  nature 
thus  incontestably  lends  itself  to  a  natural  arrange- 


Classification.  45 

ment  of  group  subordinate  to  group,  when  due 
regard  is  paid  to  degrees  of  anatomical  resemblance 
— this  mere  fact  of  itself  tells  so  weightily  in  favour 
of  descent  with  progressive  modification  in  different 
lines,  that  even  if  it  stood  alone  it  would  be  entitled 
to  rank  as  one  of  our  strongest  pieces  of  evidence. 
But,  as  we  have  seen,  it  does  not  stand  alone.  When 
we  look  beyond  this  large  and  general  fact  of  all  the 
innumerable  forms  of  life  being  thus  united  in  a 
tree-like  system  by  an  unquestionable  relationship  of 
some  kind,  to  those  smaller  details  in  the  science  of 
classification  which  have  been  found  most  useful  as 
guides  for  this  kind  of  research,  then  we  find  that  all 
these  details,  or  empirically  discovered  rules,  are 
exactly  what  we  should  have  expected  them  to  be, 
supposing  the  real  meaning  of  classification  to  have 
been  that  of  tracing  lines  of  pedigree. 

In  particular,  we  have  seen  that  the  most  archaic 
types  are  both  simpler  in  their  organization  and  more 
generalized  in  their  characters  than  are  the  more 
recent  types — a  fact  of  which  no  explanation  can  be 
'given  on  the  theory  of  special  creation.  But,  upon  the 
theory  of  natural  evolution,  we  can  without  difficulty 
understand  why  the  earlier  forms  should  have  been 
the  simpler  forms,  and  also  why  they  should  have 
been  the  most  generalized.  For  it  is  out  of  the  older 
forms  that  the  newer  must  have  grown ;  and,  as  they 
multiplied,  they  must  have  become  more  and  more 
differentiated. 

Again,  we  have  seen  that  there  is  no  correlation 
between  the  importance  of  any  structure  from  a 
classificatory  point  of  view,  and  the  importance  of  that 
structure  to  the  organism  which  presents  it.  On  the 


46  Darwin,  and  after  Darwin. 

contrary,  it  is  a  general  rule  that  "  the  less  any  part  of 
the  organization  is  concerned  with  special  habits,  the 
more  important  it  becomes  for  classification."  Now, 
from  the  point  of  view  of  special  creation  it  is  unin- 
telligible why  unity  of  ideal  should  be  most  manifested 
by  least  important  structures,  whereas  from  the  point  of 
view  of  evolution  it  is  to  be  expected  that  these  life- 
serving  structures  should  have  been  most  liable  to  diver- 
gent modification  in  divergent  lines  of  descent,  or  in 
adaptation  to  different  conditions  of  life,  while  the  trivial 
or  less  important  characters  should  have  been  allowed 
to  remain  unmodified.  Thus  we  can  now  understand 
why  all  primitive  classifications  were  wrong  in  princi- 
ple when  they  went  upon  the  assumption  that  divine 
ideals  were  best  exhibited  by  resemblances  between 
life-serving  (and  therefore  adaptive)  structures,  with 
the  result  that  whales  were  classed  with  fishes,  birds 
with  bats,  and  so  on.  Nevertheless,  these  primitive 
naturalists  were  quite  logical ;  for,  from  the  premises 
furnished  by  the  theory  of  special  creation,  it  is  much 
more  reasonable  to  expect  that  unity  of  ideal  should 
be  shown  in  plainly  adaptive  characters  than  in  trivial 
and  more  or  less  hidden  anatomical  characters.  More- 
over, long  after  biological  science  had  ceased  con- 
sciously to  follow  any  theological  theory,  the  apparent 
axiom  continued  to  be  entertained,  that  structures  of 
most  importance  to  organisms  must  also  be  structures 
of  most  importance  to  systematists.  And  when  at 
last,  in  the  present  century,  this  was  found  not  to  be 
the  case,  no  reason  could  be  suggested  why  it  was  not 
the  case.  But  now  we  are  able  fully  to  explain  this 
apparent  anomaly. 

Once    more,   we    have    seen    that    aggregates    of 


Classification.  47 

characters  presenting  resemblances  to  one  another 
have  always  been  found  to  be  of  special  importance 
as  guides  to  classification.  This,  of  course,  is  what  we 
should  have  expected,  if  the  real  meaning  of  classifica- 
tion be  that  of  tracing  lines  of  pedigree ;  but  on  the 
theory  of  special  creation  no  reason  can  be  assigned 
why  single  characters  are  not  such  sure  tokens  of 
a  natural  arrangement  as  are  aggregates  of  characters, 
however  trivial  the  latter  may  be.  For  it  is  obvious 
that  unity  of  ideal  might  have  been  even  better 
displayed  by  everywhere  maintaining  the  pattern  of 
some  one  important  structure,  than  by  doing  so  in  the 
case  of  several  unimportant  structures.  Take  an 
analogous  instance  from  human  contrivances.  Unity 
of  ideal  in  the  case  of  gun-making  would  be  shown  by 
the  same  principles  of  mechanism  running  through  all 
the  different  sizes  and  shapes  of  gun-locks,  rather  than 
by  the  ornamental  patterns  engraved  upon  the  outside ;. 
Yet  it  must  be  supposed  that  in  the  mechanisms 
assumed  to  have  been  constructed  by  special  creation, 
it  was  the  trivial  details  rather  than  the  fundamental 
principles  of  these  mechanisms  which  were  chosen  by 
the  Divinity  to  display  his  ideals. 

And  this  leads  us  to  the  next  consideration — 
namely,  that  when  in  two  different  lines  of  descent 
animals  happen  to  adopt  similar  habits  of  life,  the 
modifications  which  they  undergo  in  order  to  fit  them 
for  these  habits  often  induces  striking  resemblances  of 
structure  between  the  two  animals,  as  in  the  case  of 
whales  and  fish.  But  in  all  such  instances  it  is 
invariably  found  that  the  resemblance  is  only  super- 
ficial and  apparent :  not  anatomical  or  real.  In  other 
words,  the  resemblance  does  not  extend  further  than 


48  Darwin,  and  after  Darwin. 

it  is  necessary  that  it  should,  if  both  sets  of  organs  are 
to  be  adapted  to  perform  the  same  functions.  Now 
this,  again,  is  just  what  one  would  expect  to  find  as 
the  universal  rule  on  the  theory  of  descent,  with  modi- 
fication of  ancestral  characters.  But,  on  the  opposite 
theory  of  special  creation,  I  know  not  how  it  is  to  be 
explained  that  among  so  many  instances  of  close 
superficial  resemblance  between  creatures  belonging 
to  different  branches  of  the  tree  of  life,  there  are 
no  instances  of  any  real  or  anatomical  resemblance. 
So  far  as  their  structures  are  adapted  to  perform  a 
common  function,  there  is  in  all  such  cases  what  may 
be  termed  a  deceptive  appearance  of  some  unity  of 
ideal ;  but,  when  carefully  examined,  it  is  always 
found  that  two  apparently  identical  structures  occurring 
on  different  branches  of  the  classificatory  tree  are  in 
fact  fundamentally  different  in  respect  of  their  struc- 
tural plan. 

Lastly,  we  have  seen  that  one  of  the  guiding  prin- 
ciples of  classification  has  been  empirically  found  to 
consist  in  setting  a  high  value  on  "  chains  of  affinities." 
That  is  to  say,  naturalists  not  unfrequently  meet 
with  a  long  series  of  progressive  modifications  of  type, 
which,  although  it  cannot  be  said  that  the  continuity 
is  anywhere  broken,  at  last  leads  to  so  much  divergence 
of  character  that,  but  for  the  intermediate  links,  the 
members  at  each  end  of  the  chain  could  not  be  sus- 
pected of  being  in  any  way  related.  Well,  such  cases 
of  chains  of  affinity  obviously  tell  most  strongly  in 
favour  of  descent  with  continuous  modification  ;  while 
it  is  impossible  to  suggest  why,  if  all  the  links  were 
separately  forged  by  as  many  acts  of  special  creation, 
there  should  have  been  this  gradual  transmutation  of 


Classification.  49 

characters  carried  to  the  point  where  the  original 
creative  ideal  has  been  so  completely  transformed 
that,  but  for  the  accident  of  the  chain  being  still 
complete,  no  one  of  nature's  interpreters  could  possibly 
have  discovered  the  connexion.  For,  as  we  have  seen, 
this  is  not  a  case  in  which  any  appeal  can  be  logically 
made  to  the  argument  from  ignorance  of  divine  method; 
unless  some  independent  evidence  could  be  adduced 
in  favour  of  special  creation.  And  that  no  such  inde- 
pendent evidence  exists,  it  will  be  the  object  of  future 
chapters  to  show. 


CHAPTER    III. 

MORPHOLOGY. 

THE  theory  of  evolution  supposes  that  hereditary 
characters  admit  of  being  slowly  modified  wherever 
their  modification  will  render  an  organism  better 
suited  to  a  change  in  its  conditions  of  life.  Let 
us,  then,  observe  the  evidence  which  we  have  of  such 
adaptive  modifications  of  structure,  in  cases  where 
the  need  of  such  modification  is  apparent.  We  may 
begin  by  again  taking  the  case  of  the  whales  and 
porpoises.  The  theory  of  evolution  infers,  from  the 
whole  structure  of  these  animals,  that  their  pro- 
genitors must  have  been  terrestrial  quadrupeds  of 
some  kind,  which  gradually  became  more  and  more 
aquatic  in  their  habits.  Now  the  change  in  the 
conditions  of  their  life  thus  brought  about  would 
have  rendered  desirable  great  modifications  of  struc- 
ture. These  changes  would  have  begun  by  affecting 
the  least  typical — that  is,  the  least  strongly  inherited 
— structures,  such  as  the  skin,  claws,  and  teeth.  But, 
as  time  went  on,  the  adaptation  would  have  ex- 
tended to  more  typical  structures,  until  the  shape  of 
the  body  would  have  become  affected  by  the  bones 
and  muscles  required  for  terrestrial  locomotion  be- 
coming better  adapted  for  aquatic  locomotion,  arid 


Morphology.  5 1 

the  whole  outline  of  the  animal  more  fish-like  in 
shape.  This  is  the  stage  which  we  actually  observe 
in  the  seals,  where  the  hind  legs,  although  retaining 
all  their  typical  bones,  have  become  shortened  up 
almost  to  rudiments,  and  directed  backwards,  so  as 
to  be  of  no  use  for  walking,  while  serving  to  complete 
the  fish-like  taper  of  the  body.  (Fig.  2.)  But  in  the 
whales  the  modification  has  gone  further  than  this, 
so  that  the  hind  legs  have  ceased  to  be  apparent 
externally,  and  are  only  represented  internally — and 
even  this  only  in  some  species — by  remnants  so 
rudimentary  that  it  is  difficult  to  make  out  with 
certainty  the  homologies  of  the  bones ;  moreover, 
the  head  and  the  whole  body  have  become  com- 
pletely fish-like  in  shape.  (Fig.  3.)  But  profound 
as  are  these  alterations,  they  affect  only  those  parts 
of  the  organism  which  it  was  for  the  benefit  of  the 
organism  to  have  altered,  so  that  it  might  be  adapted 
to  an  aquatic  mode  of  existence.  Thus  the  arm, 
which  is  used  as  a  fin,  still  retains  the  bones  of  the 
shoulder,  fore-arm,  wrist,  and  fingers,  although  they 
are  all  enclosed  in  a  fin-shaped  sack,  so  as  to  render 
them  useless  for  any  purpose  other  than  swimming. 
(Fig.  4.)  Similarly,  the  head,  although  it  so  closely 
resembles  the  head  of  a  fish  in  shape,  still  retains 
the  bones  of  the  mammalian  skull  in  their  proper 
anatomical  relations  to  one  another ;  but  modified 
in  form  so  as  to  offer  the  least  possible  resistance 
to  the  water.  In  short,  it  may  be  said  that  all  the 
modifications  have  been  effected  with  the  least  pos- 
sible divergence  from  the  typical  mammalian  type, 
which  is  compatible  with  securing  so  perfect  an 
adaptation  to  a  purely  aquatic  mode  of  life. 

E    3 


54 


Darwin,  and  after  Darwin. 


Now  I  have  chosen  the  case  of  the  whale  and 
porpoise  group,  because  they  offer  so  extreme  an 
example  of  profound  modification  of  structure  in 
adaptation  to  changed  conditions  of  life.  But  the 
same  thing  may  be  seen  in  hundreds  and  hundreds 
of  other  cases.  For  instance,  to  confine  our  attention 


p< 


FIG.  4.— Paddle  of  Whale  compared  with   Hand  ,.f  Man.     Drawn 
from  nature  (£.  Coll.  Surg.  Mus.). 

to  the  arm,  not  only  is  the  limb  modified  in  the  whale 
for  swimming,  but  in  another  mammal-  the  bat— it 
is  modified  for  flying,  by  having  the  fingers  enor- 
mously elongated  and  overspread  with  a  membranous 
web. 

In  birds,  again,  the  arm  is  modified  for  flight  in 
a  wholly  different  way— the  fingers  here  being  very 


Morphology.  5  5 

short  and  all  run  together,  while  the  chief  expanse 
of  the  wing  is  composed  of  the  shoulder  and  fore- 
arm. In  frogs  and  lizards,  again,  we  find  hands 
more  like  our  own  ;  but  in  an  extinct  species  of 
flying  reptile  the  modification  was  extreme,  the 
wing  having  been  formed  by  a  prodigious  elonga- 
tion of  the  fifth  finger,  and  a  membrane  spread 
over  it  and  the  rest  of  the  hand.  (Fig.  5.)  Lastly, 
in  serpents  the  hand  and  arm  have  disappeared  alto- 
gether. 

Thus,  even  if  we  confine  our  attention  to  a  single 
organ,  how  wonderful  are  the  modifications  which 
it  is  seen  to  undergo,  although  never  losing  its  typical 
character.  Everywhere  we  find  the  distinction  be- 
tween homology  and  analogy  which  was  explained 
in  the  last  chapter — the  distinction,  that  is,  between 
correspondence  of  structure  and  correspondence  of 
function.  On  the  one  hand,  we  meet  with  structures 
which  are  perfectly  homologous  and  yet  in  no  way 
analogous  :  the  structural  elements  remain,  but  are 
profoundly  modified  so  as  to  perform  wholly  different 
functions.  On  the  other  hand,  we  meet  with  struc- 
tures which  are  perfectly  analogous,  and  yet  in  no 
way  homologous :  totally  different  structures  are 
modified  to  perform  the  same  functions.  How,  then, 
are  we  to  explain  these  things?  By  design  mani- 
fested in  special  creation,  or  by  descent  with  adaptive 
modification  ?  If  it  is  said  by  design  manifested  in 
special  creation,  we  must  suppose  that  the  Deity 
formed  an  archetypal  plan  of  certain  structures,  and 
that  he  determined  to  adhere  to  this  plan  through 
all  the  modifications  which  those  structures  exhibit. 
But,  if  so,  why  is  it  that  some  structures  are  selected 


FIG.  5. — Wing  of  Reptile,  Mammal,  and  Bird.     Drawn  from  nature 
(JSrii. 


Morphology.  57 

as  typical  and  not  others  ?  Why  should  the  vertebral 
skeleton,  for  instance,  be  tortured  into  every  conceiv- 
able variety  of  modification  in  order  to  subserve  as 
great  a  variety  of  functions  ;  while  another  structure, 
such  as  the  eye,  is  made  in  different  sub-kingdoms 
on  fundamentally  different  plans,  notwithstanding 
that  it  has  throughout  to  perform  the  same  function  ? 
Will  any  one  have  the  hardihood  to  assert  that  in 
the  case  of  the  skeleton  the  Deity  has  endeavoured 
to  show  his  ingenuity,  by  the  manifold  functions  to 
which  he  has  made  the  same  structure  subservient  ; 
while  in  the  case  of  the  eye  he  has  endeavoured  to 
show  his  resources,  by  the  manifold  structures  which 
he  has  adapted  to  serve  the  same  function  ?  If  so, 
it  becomes  a  most  unfortunate  circumstance  that, 
throughout  both  the  vegetable  and  animal  kingdoms, 
all  cases  which  can  be  pointed  to  as  showing  inge- 
nious adaptation  of  the  same  typical  structure  to  the 
performance  of  widely  different  functions — or  cases 
of  homology  without  analogy, — are  cases  which  come 
within  the  limits  of  the  same  natural  group  of  plants 
and  animals,  and  therefore  admit  of  being  equally 
well  explained  by  descent  from  a  common  ancestry ; 
while  all  cases  of  widely  different  structures  per- 
forming the  same  function — or  cases  of  analogy 
without  homology. — are  to  be  found  in  different 
groups  of  plants  or  animals,  and  are  therefore  sug- 
gestive of  independent  variations  arising  in  the  dif- 
ferent lines  of  hereditary  descent. 

To  take  a  specific  illustration.  The  octopus,  or 
devil-fish,  belongs  to  a  widely  different  class  of  animals 
from  a  true  fish  ;  and  yet  its  eye,  in  general  appear- 
ance, looks  wonderfully  like  the  eye  of  a  true  fish. 


58  Darwin,  and  after  Darwin. 

Now,  Mr.  Mivart  pointed  to  this  fact  as  a  great 
difficulty  in  the  way  of  the  theory  of  evolution  by 
natural  selection,  because  it  must  clearly  be  a  most 
improbable  thing  that  so  complicated  a  structure  as 
the  eye  of  a  fish  should  happen  to  be  arrived  at 
through  each  of  two  totally  different  lines  of  descent. 
And  this  difficulty  would,  indeed,  be  a  formidable  one 
to  the  theory  of  evolution,  if  the  similarity  were  not 
only  analogical  but  homological.  Unfortunately  for 
the  objection,  however,  Darwin  clearly  showed  in  his 
reply  that  in  no  one  anatomical  or  homologous 
feature  do  the  two  structures  resemble  one  another ; 
so  that,  in  point  of  fact,  the  two  organs  do  not 
resemble  one  another  in  any  particular  further  than  it 
is  necessary  that  they  should,  if  both  are  to  be 
analogous,  or  to  serve  the  same  function  as  organs  of 
sight.  But  now,  suppose  that  this  had  not  been  the 
case,  and  that  the  two  structures,  besides  presenting 
the  necessary  superficial  or  analogical  resemblance, 
had  also  presented  an  anatomical  or  homologous 
resemblance,  with  what  force  might  it  have  then  been 
urged, — Your  hypothesis  of  hereditary  descent  with 
progressive  modification  being  here  excluded  by  the 
fact  that  the  animals  compared  belong  to  two  widely 
different  branches  of  the  tree  of  life,  how  are  we  to 
explain  the  identity  of  type  manifested  by  these  two 
complicated  organs  of  vision?  the  only  hypothesis 
open  to  us  is  intelligent  adherence  to  an  ideal  plan  or 
mechanism.  But  as  this  cannot  now  be  urged  in  any 
comparable  case  throughout  the  whole  organic  world, 
we  may  on  the  other  hand  present  it  as  a  most  significant 
fact,  that  while  within  the  limits  of  the  same  large 
branch  of  the  tree  of  life  we  constantly  find  the  same 


Morphology.  59 

typical  structures  modified  so  as  to  perform  very 
different  functions,  we  never  find  any  of  these 
particular  types  of  structure  in  other  large  branches 
of  the  tree.  That  is  to  say,  we  never  find  typical 
structures  appearing  except  in  cases  where  their 
presence  may  be  explained  by  the  hypothesis  of 
hereditary  descent ;  while  in  thousands  of  such  cases 
we  find  these  structures  undergoing  every  conceivable 
variety  of  adaptive  modification. 

Consequently,  special  creationists  must  fall  back 
upon  another  position  and  say,  — Well,  but  it  may  have 
pleased  the  Deity  to  form  a  certain  number  of  ideal 
types,  and  never  to  have  allowed  the  structures 
occurring  in  one  type  to  appear  in  any  of  the  others. 
We  answer, — Undoubtedly  such  may  have  been  the 
case  ;  but,  if  so,  it  is  a  most  unfortunate  thing  for  your 
theory,  because  the  fact  implies  that  the  Deity  has 
planned  his  types  in  such  a  way  as  to  suggest  the 
counter-theory  of  descent.  For  instance,  it  would 
seem  most  capricious  on  the  part  of  the  Deity  to  have 
made  the  eyes  of  an  innumerable  number  of  fish  on 
exactly  the  same  ideal  type,  and  then  to  have  made 
the  eye  of  the  octopus  so  exactly  like  these  other  eyes 
in  superficial  appearance  as  to  deceive  so  accomplished 
a  naturalist  as  Mr.  Mivart,  and  yet  to  have  taken 
scrupulous  care  that  in  no  one  ideal  particular  should 
the  one  type  resemble  the  other.  However,  adopting 
for  the  sake  of  argument  this  great  assumption,  let  us 
suppose  that  God  did  lay  down  these  arbitrary  rules 
for  his  own  guidance  in  creation,  and  then  let  us  see  to 
what  the  assumption  leads.  If  the  Deity  formed  a 
certain  number  of  ideal  types,  and  determined  that 
on  no  account  should  he  allow  any  part  of  one  type 


60  Darwin,  and  after  Darwin. 

to  appear  in  any  part  of  another,  surely  we  should 
expect  that  within  the  limits  of  the  same  type  the 
same  typical  structures  should  always  be  present. 
Thus,  remember  what  efforts,  so  to  speak,  have  been 
made  to  maintain  the  uniformity  of  type  in  the  case  of 
the  fore-limb  as  previously  explained,  and  should  we 
not  expect  that  in  other  and  similar  cases  a  similar 
method  should  have  been  followed  ?  Yet  we  repeatedly 
find  that  this  is  not  the  case.  Even  in  the  whale,  as  we 
have  seen,  the  hind-limbs  are  either  altogether  absent  or 
dwindled  almost  to  nothing  ;  and  it  is  impossible  to 
see  in  what  respect  the  hind-limbs  are  of  any  less  ideal 
value  than  the  fore-limbs — which  are  carefully  pre- 
served in  all  vertebrated  animals  except  the  snakes, 
and  the  extinct  Dinornis,  where  again  we  meet  in 
this  particular  with  a  sudden  and  sublime  indiffer- 
ence to  the  maintenance  of  a  typical  structure.  (Fig.  6.)1 
Now  I  say  that  if  the  theory  of  ideal  types  is  true,  we 
have  in  these  facts  evidence  of  a  most  unreasonable  in- 
consistency. But  the  theory  of  descent  with  continued 
adaptive  modification  fully  explains  all  the  known 
cases ;  for  in  every  case  the  degree  of  divergence  from 
the  typical  structure  which  an  organism  presents 
corresponds,  in  a  general  way,  with  the  length  of  time 
during  which  the  divergence  has  been  going  on. 
Thus  we  scarcely  ever  meet  with  any  great  departure 
from  the  typical  form  with  respect  to  one  of  the 
organs,  without  some  of  the  other  organs  being  so  far 
modified  as  of  themselves  to  indicate,  on  the  sup- 

1  It  is,  however,  probable  that  all  species  of  the  genus  retained  a  tiny 
rudiment  of  wings  in  greatly  dwindled  scapulo-coracoid  bones.  And 
Mr.  H.  O.  Forbes  has  detected,  in  a  recently  exhumed  specimen  of  the 
latter,  an  indication  of  the  glenoid  cavity,  for  the  articulation  of  an 
extremely  aborted  humerus.  (See  Nature,  Jan.  I4th,  1892.) 


FIG.  6. — Skeleton  of  Dinornis  g ravis,  -fa  nat.  size.  Drawn  from  nature 
(Brit.  Mus.\  As  separate  cuts  on  a  larger  scale  are  shown,  ist,  the  sternum, 
as  this  appears  in  mounted  skeletons,  and,  2nd,  the  same  in  profile,  with  its 
(hypothetical)  scapulo-coracoid  attached. 


62  Darwin,  and  after  Darwin. 

position  of  descent  with  modification,  that  the  animal 
or  plant  must  have  been  subject  to  the  modifying 
influences  for  an  enormously  long  series  of  generations. 
And  this  combined  testimony  of  a  number  of  organs 
in  the  same  organism  is  what  the  theory  of  descent 
would  lead  us  to  expect,  while  the  rival  theory  of 
design  can  offer  no  explanation  of  the  fact,  that  when 
one  organ  shows  a  conspicuous  departure  from  the 
supposed  ideal  type,  some  of  the  other  organs  in  the 
same  organism  should  tend  to  keep  it  company  by 
doing  likewise. 

As  an  illustration  both  of  this  and  of  other  points 
which  have  been  mentioned,  I  may  draw  attention  to 
what  seems  to  me  a  particularly  suggestive  case.  So- 
called  soldier-  or  hermit-crabs,  are  crabs  which  have 
adopted  the  habit  of  appropriating  the  empty  shells 
of  mollusks.  In  association  with  this  peculiar  habit, 
the  structure  of  these  animals  differs  very  greatly  from 
that  of  all  other  crabs.  In  particular,  the  hinder  part 
of  the  body,  which  occupies  the  mollusk-shell,  and 
which  therefore  has  ceased  to  require  any  hard  cover- 
ing of  its  own,  has  been  suffered  to  lose  its  calcareous 
integument,  and  presents  a  soft  fleshy  character,  quite 
unlike  that  of  the  more  exposed  parts  of  the  animal. 
Moreover,  this  soft  fleshy  part  of  the  creature  is 
specially  adapted  to  the  particular  requirements  of 
the  creature  by  having  its  lateral  appendages — i.e. 
appendages  which  in  other  Crustacea  perform  the 
function  of  legs  —  modified  so  as  to  act  as  claspers  to 
the  inside  of  the  mollusk-shell ;  while  the  tail-end  of 
the  part  in  question  is  twisted  into  the  form  of  a  spiral, 
which  fits  into  the  spiral  of  the  mollusk-shell.  Now, 
in  Keeling  Island  there  is  a  large  kind  of  crab  called 


Morphology.  63 

Birgtts  latro,  which  lives  upon  land  and  there  feeds 
upon  cocoa-nuts.  The  whole  structure  of  this  crab,  it 
seems  to  me,  unmistakeably  resembles  the  structure 
of  a  hermit-crab  (see  drawings  on  the  next  page, 
Fig.  7).  Yet  this  crab  neither  lives  in  the  shell  of 
a  mollusk,  nor  is  the  hinder  part  of  its  body  in  the  soft 
and  fleshy  condition  just  described  :  on  the  contrary,  it 
is  covered  with  a  hard  integument  like  all  the  other 
parts  of  the  animal.  Consequently,  I  think  we  may  infer 
that  the  ancestors  of  Birgns  were  hermit-crabs  living 
in  mollusk-shells  ;  but  that  their  descendants  grad- 
ually relinquished  this  habit  as  they  gradually  became 
more  and  more  terrestrial,  while,  concurrently  with 
these  changes  in  habit,  the  originally  soft  posterior 
parts  acquired  a  hard  protective  covering  to  take  the 
place  of  that  which  was  formerly  supplied  by  the 
mollusk-shell.  So  that,  if  so,  we  now  have,  within  the 
limits  of  a  single  organism,  evidence  of  a  whole  series 
of  morphological  changes  in  the  past  history  of  its 
species.  First,  there  must  have  been  the  great  change 
from  an  ordinary  crab  to  a  hermit-crab  in  all  the 
respects  previously  pointed  out.  Next,  there  must 
have  been  the  change  back  again  from  a  hermit-crab 
to  an  ordinary  crab,  so  far  as  living  without  the  ne- 
cessity of  a  mollusk-shell  is  concerned.  From  an 
evolutionary  point  of  view,  therefore,  we  appear  to  have 
in  the  existing  structure  of  Birgus  a  morphological 
record  of  all  these  changes,  and  one  which  gives  us  a 
reasonable  explanation  of  why  the  animal  presents  the 
extraordinary  appearance  which  it  does.  But,  on  the 
theory  of  special  creation,  it  is  inexplicable  why  this 
land-crab  should  have  been  formed  on  the  pattern  of 
a  hermit-crab,  when  it  never  has  need  to  enter  the  shell 


Morphology.  65 

of  a  mollusk.  In  other  words,  its  peculiar  structure 
is  not  specially  in  keeping  with  its  present  habits, 
although  so  curiously  -allied  to  the  similar  structure 
of  certain  other  crabs  of  totally  different  habits,  in 
relation  to  which  the  peculiarities  are  of  plain  and 
obvious  significance. 

I  will  devote  the  remainder  of  this  chapter  to 
considering  another  branch  of  the  argument  from 
morphology,  to  which  the  case  of  Birgns  serves  as 
a  suitable  introduction:  I  mean  the  argument  from 
rudimentary  structures. 

Throughout  both  the  animal  and  vegetable  king- 
doms we  constantly  meet  with  dwarfed  and  useless 
representatives  of  organs,  which  in  other  and  allied 
kinds  of  animals  and  plants  are  of  large  size  and 
functional  utility.  Thus,  for  instance,  the  unborn 
whale  has  rudimentary  teeth,  which  are  never  des- 
tined to  cut  the  gums  ;  and  throughout  its  life  this 
animal  retains,  in  a  similarly  rudimentary  condition, 
a  number  of  organs  which  never  could  have  been  of  use 
to  any  kind  of  creature  save  a  terrestrial  quadruped. 
The  whole  anatomy  of  its  internal  ear,  for  example, 
has  reference  to  hearing  in  air — or.  as  Hunter  long  ago 
remarked,  "  is  constructed  upon  the  same  principle  as 
in  the  quadruped'';  yet,  as  Owen  says,  "the  outer 
opening  and  passage  leading  therefrom  to  the  tym- 
panum can  rarely  be  affected  by  sonorous  vibrations 
of  the  atmosphere,  and  indeed  they  are  reduced,  or 
have  degenerated,  to  a  degree  which  makes  it  difficult 
to  conceive  how  such  vibrations  can  be  propagated  to 
the  ear-drum  during  the  brief  moments  in  which  the 
opening  may  be  raised  above  the  water." 

*  F 


66  Darwin,  and  after  Darwin. 

Now,  rudimentary  organs  of  this  kind  are  of  such 
frequent  occurrence,  that  almost  every  species  presents 
one  or  more  of  them — usually,  indeed,  a  considerable 
number.  How,  then,  are  they  to  be  accounted  for  ? 
Of  course  the  theory  of  descent  with  adaptive  modifi- 
cation has  a  simple  answer  to  supply — namely,  that 
when,  from  changed  conditions  of  life,  an  organ  which 
was  previously  useful  becomes  useless,  it  will  be  suf- 
fered to  dwindle  away  in  successive  generations,  under 
the  influence  of  certain  natural  causes  which  we  shall 
have  to  consider  in  future  chapters.  On  the  other 
hand,  the  theory  of  special  creation  can  only  maintain 
that  these  rudiments  are  formed  for  the  sake  of  ad- 
hering to  an  ideal  type.  Now,  here  again  the  former 
theory  appears  to  be  triumphant  over  the  latter  ;  for, 
without  waiting  to  dispute  the  wisdom  of  making 
dwarfed  and  useless  structures  merely  for  the  whim- 
sical motive  assigned,  surely  if  such  a  method  were 
adopted  in  so  many  cases,  we  should  expect  that  in 
consistency  it  would  be  adopted  in  all  cases.  This 
reasonable  expectation,  however,  is  far  from  being 
realized.  We  have  already  seen  that  in  numberless 
cases,  such  as  that  of  the  fore-limbs  of  serpents,  no 
vestige  of  a  rudiment  is  present.  But  the  vacillating 
policy  in  the  matter  of  rudiments  does  not  end  here ; 
for  it  is  shown  in  a  still  more  aggravated  form  where 
within  the  limits  of  the  same  natural  group  of  or- 
ganisms a  rudiment  is  sometimes  present  and  some- 
times absent.  For  instance,  although  in  nearly  all  the 
numerous  species  of  snakes  there  are  no  vestiges  of 
limbs,  in  the  Python  we  find  very  tiny  rudiments  of  the 
hind-limbs.  (Fig.  8.)  Now,  is  it  a  worthy  conception  of 
Deity  that,  while  neglecting  to  maintain  his  unity  of 


Morphology. 


67 


ideal  in  the  case  of  nearly  all  the  numerous  species 
of  snakes,  he  should  have  added  a  tiny  rudiment  in 
the  case  of  the  Python— and  even  in  that  case  should 
have  maintained  his  ideal  very  inefficiently,  inas- 
much as  only  two  limbs,  instead  of  four,  are  repre- 
sented ?  How  much  more  reasonable  is  the  natura- 

P  Y  TH  oN . 


FlG.  8. — Rudimentary  or  vestigial  hind-limbs  of  Python,  as  exhibited 
in  the  skeleton  ind  on  the  external  surface  of  the  animal.  Drawn  from 
nature,  \  nat.  size  {Zoological  Gardens). 

listic  interpretation ;  for  here  the  very  irregularity  of 
their  appearance  in  different  species,  which  constitutes 
rudimentary  structures  one  of  the  crowning  difficulties 
to  the  theory  of  special  design,  furnishes  the  best 
possible  evidence  in  favour  of  hereditary  descent  ; 
seeing  that  this  irregularity  then  becomes  what  may 
be  termed  the  anticipated  expression  of  progressive 
F  2 


68  Darwin,  and  after  Darwin. 

dwindling  due  to  inutility.  Thus,  for  example,  to 
return  to  the  case  of  wings,  we  have  already  seen 
that  in  an  extinct  genus  of  bird,  Dinornis,  these 
organs  were  reduced  to  such  an  extent  as  to  leave 
it  still  doubtful  whether  so  much  as  the  tiny  rudiment 
hypothetically  supplied  to  Fig.  6  (p.  61)  was  present 
in  all  the  species.  And  here  is  another  well-known 
case  of  another  genus  of  still  existing  bird,  which,  as 
was  the  case  with  Dinornis,  occurs  only  in  New 
Zealand.  (Fig.  9.)  Upon  this  island  there  are  no  four- 
footed  enemies — either  existing  or  extinct — to  escape 
from  which  the  wings  of  birds  would  be  of  any  service. 
Consequently  we  can  understand  why  on  this  island 
we  should  meet  with  such  a  remarkable  dwindling 
away  of  wings. 

Similarly,  the  logger-headed  duck  of  South  America 
can  only  flap  along  the  surface  of  the  water,  having 
its  wings  considerably  reduced  though  less  so  than 
the  Apteryx  of  New  Zealand.  But  here  the  interesting 
fact  is  that  the  young  birds  are  able  to  fly  perfectly 
well.  Now,  in  accordance  with  a  general  law  to  be 
considered  in  a  future  chapter,  the  life-history  of  an 
individual  organism  is  a  kind  of  condensed  recapitu- 
lation of  the  life-history  of  its  species.  Consequently, 
we  can  understand  why  the  little  chickens  of  the 
logger-headed  duck  are  able  to  fly  like  all  other  ducks, 
while  their  parents  are  only  able  to  flap  along  the 
surface  of  the  water. 

Facts  analogous  to  this  reduction  of  wings  in  birds 
which  have  no  further  use  for  them,  are  to  be  met 
with  also  in  insects  under  similar  circumstances. 
Thus,  there  are  on  the  island  of  Madeira  somewhere 
between  500  and  600  species  of  beetles,  which  are  in 


Morphology. 


69 


large  part  peculiar  to  that  island,  though  related  to 
other — and  therefore  presumably  parent — species  on 
the  neighbouring  continent.  Now,  no  less  than  200 
species — or  nearly  half  the  whole  number — are  so  far 
deficient  in  wings  that  they  cannot  fly.  And,  if  we 


FIG.  y. — Apteryx  Australis.  Drawn  from  life  in  the  Zoological 
Gardens,  \  nat.  size.  The  external  wing  is  drawn  to  a  scale  in  the  upper 
part  of  the  cut.  The  surroundings  are  supplied  from  the  most  recent 
descriptions. 

disregard  the  species  which  are  not  peculiar  to  the 
island — that  is  to  say,  all  the  species  which  likewise 
occur  on  the  neighbouring  continent,  and  therefore, 
as  evolutionists  conclude,  have  but  recently  migrated 
to  the  island,  —  we  find  this  very  remarkable  proportion. 
There  are  altogether  29  peculiar  genera,  and  out  of 


70  Darwin,  and  after  Darwin. 

these  no  less  than  23  have  all  their  species  in  this 
condition. 

Similar  facts  have  been  recently  observed  by  the 
Rev.  A.  E.  Eaton  with  respect  to  insects  inhabiting 
Kerguelen  Island.  All  the  species  which  he  found 
on  the  island— viz.  a  moth,  several  flies,  and  numerous 
beetles — he  found  to  be  incapable  of  flight;  and 
therefore, as  Wallace  observes,  "as  these  insects  could 
hardly  have  reached  the  islands  in  a  wingless  state, 
even  if  there  were  any  other  known  land  inhabited  by 
them,  which  there  is  not,  we  must  assume  that,  like 
the  Madeiran  insects,  they  were  originally  winged, 
and  lost  their  power  of  flight  because  its  possession 
was  injurious  to  them  " — Kerguelen  Island  being  "  one 
of  the  stormiest  places  on  the  globe,"  and  therefore  a 
place  where  insects  could  rarely  afford  to  fly  without 
incurring  the  danger  of  being  blown  out  to  sea. 

Here  is  another  and  perhaps  an  even  more  suggestive 
class  of  facts. 

It  is  now  many  years  ago  since  the  editors  of 
Sillimaris  Journal  requested  the  late  Professor  Agassiz 
to  give  them  his  opinion  on  the  following  question. 
In  a  certain  dark  subterranean  cave,  called  the 
Mammoth  cave,  there  are  found  some  peculiar  species 
of  blind  fishes.  Now  the  editors  of  Sillimans  Journal 
wished  to  know  whether  Prof.  Agassiz  would  hold 
that  these  fish  had  been  specially  created  in  these 
caves,  and  purposely  devoided  of  eyes  which  could 
never  be  of  any  use  to  them  ;  or  whether  he  would 
allow  that  these  fish  had  probably  descended  from 
other  species,  but,  having  got  into  the  dark  cave, 
gradually  lost  their  eyes  through  disuse.  Prof. 
Agassiz,  who  was  a  believer  in  special  creation, 


Morphology.  7 1 

allowed  that  this  ought  to  constitute  a  crucial  test  as 
between  the  two  theories  of  special  design  and  here- 
ditary descent.  "  If  physical  circumstances,"  he  said, 
"ever  modified  organized  beings,  it  should  be  easily 
ascertained  here."  And  eventually  he  gave  it  as  his 
opinion,  that  these  fish  "  were  created  under  the  cir- 
cumstances in  which  they  now  live,  within  the  limits 
over  which  they  now  range,  and  with  the  structural 
peculiarities  which  now  characterise  them." 

Since  then  a  great  deal  of  attention  has  been  paid 
to  the  fauna  of  this  Mammoth  cave,  and  also  to  the 
faunas  of  other  dark  caverns,  not  only  in  the  New, 
but  also  in  the  Old  World.  In  the  result,  the  fol- 
lowing general  facts  have  been  fully  established. 

(1)  Not  only  fish,  but  many  representatives  of  other 
classes,  have  been  found  in  dark  caves. 

(2)  Wherever  the  caves  are  totally  dark,  all  the 
animals  are  blind. 

(3)  If  the  animals  live  near  enough  to  the  entrance 
to  receive  some  degree  of  light,  they  may  have  large 
and  lustrous  eyes. 

(4)  In  all  cases  the  species  of  blind  animals  are 
closely  allied  to  species  inhabiting  the  district  where 
the  caves  occur;    so  that  the  blind  species  inhabit- 
ing  American  caves  are  closely  allied   to  American 
species,  while  those  inhabiting   European   caves   are 
closely  allied  to  European  species. 

(5)  In  nearly  all  cases  structural  remnants  of  eyes 
admit  of  being  detected,  in  various  degrees  of  obsoles- 
cence.    In  the  case  of  some  of  the  crustaceans  of  the 
Mammoth  cave  the  foot-stalks  of  the  eyes  are  present, 
although  the  eyes  themselves  are  entirely  absent. 

Now,  it  is  evident  that  all  these  general  facts  are  in 


72  Darwin,  and  after  Darwin. 

full  agreement  with  the  theory  of  evolution,  while 
they  offer  serious  difficulties  to  the  theory  of  special 
creation.  As  Darwin  remarks,  it  is  hard  to  imagine 
conditions  of  life  more  similar  than  those  furnished  by 
deep  limestone  caverns  under  nearly  the  same  climate 
in  the  two  continents  of  America  and  Europe;  so 
that,  in  accordance  with  the  theory  of  special  creation, 
very  close  similarity  in  the  organizations  of  the  two 
sets  of  faunas  might  have  been  expected.  But, 
instead  of  this,  the  affinities  of  these  two  sets  of 
faunas  are  with  those  of  their  respective  continents — 
as  of  course  they  ought  to  be  on  the  theory  of 
evolution.  Again,  what  would  have  been  the  sense 
of  creating  useless  foot-stalks  for  the  imaginary  sup- 
port of  absent  eyes,  not  to  mention  aJl  the  other 
various  grades  of  degeneration  in  other  cases  ?  So 
that,  upon  the  whole,  if  we  agree  with  the  late  Prof. 
Agassiz  in  regarding  these  cave  animals  as  furnishing 
a  crucial  test  between  the  rival  theories  of  creation 
and  evolution,  we  must  further  conclude  that  the 
whole  body  of  evidence  which  they  now  furnish  is 
weighing  on  the  side  of  evolution. 

So  much,  then,  for  a  few  special  instances  of  what 
Darwin  called  rudimentary  structures,  but  what  may 
be  more  descriptively  designated — in  accordance  with 
the  theory  of  descent — obsolescent  or  vestigial  struc- 
tures. It  is,  however,  of  great  importance  to  add  that 
these  structures  are  of  such  general  occurrence  through- 
out both  the  vegetable  and  animal  kingdoms,  that,  as 
Darwin  has  observed,  it  is  almost  impossible  to  point 
to  a  single  species  which  does  not  present  one  or 
more  of  them.  In  other  words,  it  is  almost  impos- 
sible to  find  a  single  species  which  does  not  in  this 


Morphology.  73 

way  bear  some  record  of  its  own  descent  from  other 
species  ;  and  the  more  closely  the  structure  of  any 
species  is  examined  anatomically,  the  more  numerous 
are  such  records  found  to  be.  Thus,  for  example,  of 
all  organisms  that  of  man  has  been  most  minutely 
investigated  by  anatomists ;  and  therefore  I  think  it 
will  be  instructive  to  conclude  this  chapter  by  giving 
a  list  of  the  more  noteworthy  vestigial  structures 
which  are  known  to  occur  in  the  human  body.  I  will 
take  only  those  which  are  found  in  adult  man,  reserving 
for  the  next  chapter  those  which  occur  in  a  transitory 
manner  during  earlier  periods  of  his  life.  But,  even  as 
thus  restricted,  the  number  of  obsolescent  structures 
which  we  all  present  in  our  own  persons  is  so  remark- 
able, that  their  combined  testimony  to  our  descent  from 
a  quadrumanous  ancestry  appears  to  me  in  itself  con- 
clusive. I  mean,  that  even  if  these  structures  stood 
alone,  or  apart  from  any  more  general  evidences  of 
our  family  relationships,  they  would  be  sufficient  to 
prove  our  parentage.  Nevertheless,  it  is  desiiable  to 
remark  that  of  course  these  special  evidences  which  I 
am  about  to  detail  do  not  stand  alone.  Not  only  is 
there  the  general  analogy  furnished  by  the  general 
proof  of  evolution  elsewhere,  but  there  is  likewise 
the  more  special  correspondence  between  the  whole 
of  our  anatomy  and  that  of  our  nearest  zoological 
allies.  Now  the  force  of  this  latter  consideration  is  so 
enormous,  that  no  one  who  has  not  studied  human 
anatomy  can  be  in  a  position  to  appreciate  it.  For 
without  special  study  it  is  impossible  to  form  any  ad- 
equate idea  of  the  intricacy  of  structure  which  is  pre- 
sented by  the  human  form.  Yet  it  is  found  that  this 
enormously  intricate  organization  is  repeated  in  all  its 


74  Darwin,  and  after  Darwin. 

details  in  the  bodies  of  the  higher  apes.  There  is  no 
bone,  muscle,  nerve,  or  vessel  of  any  importance  in  the 
one  which  is  not  answered  to  by  the  other.  Hence 
there  are  hundreds  of  thousands  of  instances  of  the 
most  detailed  correspondence,  without  there  being 
any  instances  to  the  contrary,  if  we  pay  due  regard 
to  vestigial  characters.  The  entire  corporeal  structure 
of  man  is  an  exact  anatomical  copy  of  that  which  we 
find  in  the  ape. 

My  object,  then,  here  is  to  limit  attention  to  those 
features  of  our  corporeal  structure  which,  having 
become  useless  on  account  of  our  change  in  attitude 
and  habits,  are  in  process  of  becoming  obsolete,  and 
therefore  occur  as  mere  vestigial  records  of  a  former 
state  of  things.  For  example,  throughout  the  verte- 
brated  series,  from  fish  to  mammals,  there  occurs  in 
the  inner  corner  of  the  eye  a  semi-transparent  eye-lid, 
which  is  called  the  nictitating  membrane.  The  object 
of  this  structure  is  to  sweep  rapidly,  every  now  and 
then,  over  the  external  surface  of  the  eye.  apparently 
in  order  to  keep  the  surface  clean.  But  although  the 
membrane  occurs  in  all  classes  of  the  sub-kingdom, 
it  is  more  prevalent  in  some  than  in  others— e.g. 
in  birds  than  in  mammals.  Even;  however,  where  it 
does  not  occur  of  a  size  and  mobility  to  be  of  any  use, 
it  is  usually  represented,  in  animals  above  fishes,  by  a 
functionless  rudiment,  as  here  depicted  in  the  case  of 
man.  (Fig.  10.) 

Now  the  organization  of  man  presents  so  many 
vestigial  structures  thus  referring  to  various  stages  of 
his  long  ancestral  history,  that  it  would  be  tedious  so 
much  as  to  enumerate  them.  Therefore  I  will  yet 
further  limit  the  list  of  vestigial  structures  to  be  given 


tfflff 


FIG.  io.— Illustrations  of  the  nictitating  membrane  in  the  various  animals  named 
drawn  from  nature.  The  letter  N  indicates  the  membrane  in  each  case.  In  man 
it  is  called  the  plica  semilunaris,  and  is  represented  in  the  two  lower  drawings 
under  this  name.  In  the  case  of  the  shark  (Galeus)  the  muscular  mechanism  is 
shown  as  dissected. 


j6  Darwin,  and  after  Darwin. 

as  examples,  by  not  only  restricting  these  to  cases 
which  occur  in  our  own  organization  ;  but  of  them  I 
shall  mention  only  such  as  refer  us  to  the  very  last 
stage  of  our  ancestral  history — viz.  structures  which 


FlG.  11. — Rudimentary,  or  vestigial  and  useless,  muscles  of  the 
human  ear.     (From  Grays  Anatouiy.} 

have  become  obsolescent  since  the  time  when  our  dis- 
tinctively human  branch  of  the  family  tree  diverged  from 
that  of  our  immediate  forefathers,  the  Quadrumana. 

(i)  Muscles  of  the  external  car,— These,  which  are 
of  large  size  and  functional  use  in  quadrupeds,  we 


Morphology.  7  7 

retain  in  a  dwindled  and  useless  condition  (Fig.  u). 
This  is  likewise  the  case  in  anthropoid  apes ;  but  in 
not  a  few  other  Quadrumana  (e  g.  baboons,  macacus 
magots,  &c.)  degeneration  has  not  proceeded  so  far, 
and  the  ears  are  voluntarily  moveable. 

(2)  Panniculus   carnosis. — A  large  number  of  the 
mammalia  are  able  to  move  their  skin  by  means  of 
sub-cutaneous  muscle— as  we  see,  for  instance,  in  a 
horse,    when    thus    protecting    himself    against    the 
sucking  of  flies.     We,  in  common   with  the  Quad- 
rumana, possess  an  active  remnant  of  such  a  muscle  in 
the  skin  of  the  forehead,  whereby  we  draw  up  the 
eyebrows ;    but  we  are  no  longer  able  to  use  other 
considerable  remnants  of  it,  in  the  scalp  and  elsewhere, 
— or,  more  correctly,  it  is  rarely  that  we  meet  with 
persons   who   can.      But    most   of  the    Quadrumana 
(including   the  anthropoids)  are  still  able  to  do  so. 
There  are  also  many  other  vestigial  muscles,  which 
occur  only  in  a  small  percentage  of  human  beings, 
but  which,  when  they  do  occur,  present  unmistakeable 
homologies  with  normal  muscles  in  some  of  the  Quad- 
rumana and  still  lower  animals  l. 

(3)  Feet. — It   is   observable  that  in  the  infant  the 
feet  have  a  strong  deflection  inwards,  so  that  the  soles 
in   considerable    measure    face    one    another.      This 
peculiarity,  which  is  even  more  marked  in  the  embryo 
than  in  the  infant  (see  p.  153),  and  which  becomes 
gradually  less  and   less  conspicuous  even  before  the 
child  begins  to  walk,  appears  to  me  a  highly  sugges- 
tive peculiarity.    For  it  plainly  refers  to  the  condition 

1  See  especially  Mr.  John  Wood's  papers,  Proc.  R.  S.,  xiii  to  xvi,  and 
xviii ;  also  Journ.  Anat.,  \  and  iii.  In  this  connexion  Darwin  refers 
to  M.  Richard,  Annls.  d.  Sc.  Nat.  Zoolg.,  torn,  xviii,  p.  13,  1852. 


78  Darwin,  and  ajter  Darwin. 

of  things  in  the  Quadrumana,  seeing  that  in  all  these 
animals  the  feet  are  similarly  curved  inwards,  to 
facilitate  the  grasping  of  branches.  And  even  when 
walking  on  the  ground  apes  and  monkeys  employ  to 
a  great  extent  the  outside  edges  of  their  feet,  as  does 


FlG.  12. — Portrait  of  a  young  male  gorilla  ^after  Hartman 


also  a  child  when  learning  to  walk.  The  feet  of  a 
young  child  are  also  extraordinarily  mobile  in  all 
directions,  as  are  those  of  apes.  In  order  to  show 
these  points,  I  here  introduce  comparative  drawings 
of  a  young  ape  and  the  portrait  of  a  young  male 
child.  These  drawings,  moreover,  serve  at  the 


Morphology.  79 

same  time  to  illustrate  two  other  vestigial  characters, 
which  have  often  been  previously  noticed  with  regard 
to  the  infant's  foot.  I  allude  to  the  incurved  form  of 
the  legs;  and  the  lateral  extension  of  the  great  toe, 
whereby  it  approaches  the  thumb-like  character  of 


FlG.  13. — Portrait  of  a  young  male  child.  Photographed  from  life, 
when  the  mobile  feet  were  for  a  short  time  at  rest  in  a  position  of 
extreme  inflection. 

this  organ  in  the  Quadrumana.  As  in  the  case  of 
the  incurved  position  of  the  legs  and  feet,  so  in  this 
case  of  the  lateral  extensibility  of  the  great  toe,  the 
peculiarity  is  even  more  marked  in  embryonic  than  in 
infant  life.  For,  as  Prof.  Wyman  has  remarked  with 
regard  to  the  foetus  when  about  an  inch  in  length, 


8o  Darwin,  and  after  Darwin. 

11  The  great  toe  is  shorter  than  the  others ;  and,  instead 
of  being  parallel  to  them,  is  projected  at  an  angle  from 
the  side  of  the  foot,  thus  corresponding  with  the  per- 
manent condition  of  this  part  in  the  Quadrumana1." 
So  that  this  organ,  which,  according  to  Owen,  "is 
perhaps  the  most  characteristic  peculiarity  in  the 
human  structure,"  when  traced  back  to  the  early 
stages  of  its  development,  is  found  to  present  a 
notably  less  degree  of  peculiarity. 

(4)  Hands. — Dr.  Louis  Robinson  has  recently 
observed  that  the  grasping  power  of  the  whole  human 
hand  is  so  surprisingly  great  at  birth,  and  during  the 
first  few  weeks  of  infancy,  as  to  be  far  in  excess  of 
present  requirements  on  the  part  of  a  young  child. 
Hence  he  concludes  that  it  refers  us  to  our  quadru- 
manous  ancestry — the  young  of  anthropoid  apes  being 
endowed  with  similar  powers  of  grasping,  in  order  to 
hold  on  to  the  hair  of  the  mother  when  she  is  using 
her  arms  for  the  purposes  of  locomotion.  This  in- 
ference appears  to  me  justifiable,  inasmuch  as  no 
other  explanation  can  be  given  of  the  comparatively 
inordinate  muscular  force  of  an  infant's  grip.  For 
experiments  showed  that  very  young  babies  are  able 
to  support  their  own  weight,  by  holding  on  to  a 
horizontal  bar,  for  a  period  varying  from  one  half  to 
more  than  two  minutes  2.  With  his  kind  permission 
I  here  reproduce  one  of  Dr.  Robinson's  instantaneous, 
and  hitherto  unpublished,  photographs  of  a  very  young 
infant.  This  photograph  was  taken  after  the  above 
paragraph  (3)  was  written,  and  I  introduce  it  here 
because  it  serves  to  show  incidentally— and  perhaps 

1  Proc.  Nat.  Hist.  Soc.,  Boston,  1863. 
1  Nineteenth  Century,  November,  1891, 


Morphology. 


81 


even  better  than  the  preceding  figure — the  points 
there  mentioned  with  regard  to  the  feet  and  great 
toes.  Again,  as  Dr.  Robinson  observes,  the  attitude, 
and  the  disproportionately  large  development  of  the 
arms  as  compared  with  the  legs  give  all  the  photo- 
graphs a  striking  resemblance  to  a  picture  of  the 


Fig.  14. — An  infant,  three  weeks  old,  supporting  its  own  weight  foi 
over  two  minutes.  The  attitude  of  the  lower  limbs,  feet,  and  toes, 
is  strikingly  simian.  Reproduced  from  an  instantaneous  photograph, 
kindly  given  for  the  purpose  by  Dr.  L.  Robinson. 

chimpanzee  "Sally"  at  the  Zoological  Gardens.  For 
"  invariably  the  thighs  are  bent  nearly  at  right  angles 
to  the  body,  and  in  no  case  did  the  lower  limbs  hang 
down  and  take  the  attitude  of  the  erect  position."  He 
adds,  "  In  many  cases  no  sign  of  distress  is  evinced, 
*  G 


82 


Darwin,  and  after  Darwin. 


and  no  cry  uttered,  until  the  grasp  begins  to  give 
way." 

(5)  Tail, — The  absence  of  a  tail  in  man  is  popularly 
supposed  to  constitute  a  difficulty  against  the  doctrine 
of  his  quadrumanous  descent.  As  a  matter  of  fact, 
however,  the  absence  of  an  external  tail  in  man  is 


MAN 


GORILLA 


FIG.  15. — Sacrum  of  Gorilla  compared  with  that  of  Man,  showing  the 
rudimentary  tail-bones  of  each.  Drawn  from  nature  (A'.  Coll.  Surg. 
A/us.). 

precisely  what  this  doctrine  would  expect,  seeing  that 
the  nearest  allies  of  man  in  the  quadrumanous  series 
are  likewise  destitute  of  an  external  tail.  Far,  then, 
from  this  deficiency  in  man  constituting  any  difficulty 
to  be  accounted  for,  if  the  case  were  not  so — i.e.  if  man 
did  possess  an  external  tail, — the  difficulty  would  be 


Morphology.  83 

to  understand  how  he  had  managed  to  retain  an 
organ  which  had  been  renounced  by  his  most  recent 
ancestors.  Nevertheless,  as  the  anthropoid  apes  con- 
tinue to  present  the  rudimentary  vestiges  of  a  tail 
in  a  few  caudal  vertebrae  below  the  integuments,  we 
might  well  expect  to  find  a  similar  state  of  matters  in 
the  case  of  man.  And  this  is  just  what  we  do  find,  as 
a  glance  at  these  two  comparative  illustrations  will 
show.  (Fig.  15.)  Moreover,  during  embryonic  life, 
both  of  the  anthropoid  apes  and  of  man,  the  tail  much 


FIG.  16. — Diagrammatic  outline  of  the  human  embryo  when  about 
seven  weeks  old,  showing  the  relations  of  the  limbs  and  tail  to  the 
trunk  (after  Allen  Thomson),  r,  the  radial,  and  «,  the  ulnar,  border  of 
the  hand  and  fore-arm ;  /,  the  tibial,  and  f,  the  fibular,  border  of  the 
foot  and  lower  leg ;  au,  ear  j  s,  spinal  cord ;  v,  umbilical  cord ;  b,  branchial 
gill-slits;  c,  tail. 

more  closely  resembles  that  of  the  lower  kinds  of 
quadrumanous  animals  from  which  these  higher  re- 
presentatives of  the  group  have  descended.  For  at 
a  certain  stage  of  embryonic  life  the  tail,  both  of  apes 
and  of  human  beings,  is  actually  longer  than  the  legs 
(see  Fig.  16).  And  at  this  stage  of  development, 
also,  the  tail  admits  of  being  moved  by  muscles 
which  later  on  dwindle  away.  Occasionally,  however, 
G  2 


84 


Darwin,  and  after  Darwin. 


these  muscles  persist,  and  are  then  described  by 
anatomists  as  abnormalities.  The  following  illustra- 
tions serve  to  show  the  muscles  in  question,  when  thus 
found  in  adult  man. 


FIG.  17. — Front  and  back  view  of  adult  human  sacrum,  showing 
abnormal  persistence  of  vestigial  tail-muscles.  (The  first  drawing  is 
copied  from  Prof.  Watson's  paper  in  Journl.  Anat.  and  PhysioL,  vol. 
79  :  the  second  is  compiled  from  different  specimens.) 


(6)  Vermiform  Appendix  of  the  Ccecum. — This  is  of 
large  size  and  functional  use  in  the  process  of  digestion 
among  many  herbivorous  animals ;  while  in  man  it  is 
not  only  too  small  to  serve  any  such  purpose,  but  is 
even  a  source  of  danger  to  life — many  persons  dying 
every  year  from  inflammation  set  up  by  the  lodge- 
ment in  this  blind  tube  of  fruit-stones,  &c. 

In  the  orang  it  is  longer  than  in  man  (Fig.  1 8),  as 


Morphology. 


FIG.  1 8. — Appendix  vermiformis  in  Orang  and  in  Man.  Drawn  from 
dried  inflated  specimens  in  the  Cambridge  Museum  by  Mr.  J.  J.  Lis- 
ter. //,  ilium;  Co,  colon;  C,  ccecum;  W,  a  window  cut  in  the  wall 
of  the  ccecum ;  x  x  x,  the  appendix. 


FlG.  19. — The  same,  showing  variation  in  the  Orang.     Drawn  fri 
a  specimen  in  the  Museum  of  the  Royal  College  of  Surgeons. 


86  Darwin,  and  after  Darwin. 

it  is  also  in  the  human  foetus  proportionally  compared 
with  the  adult.  (Fig.  19.)  In  some  of  the  lower  herbi- 
vorous animals  it  is  longer  than  the  entire  body. 

Like  vestigial  structures  in  general,  however,  this  one 
is  highly  variable.  Thus  the  above  cut  (Fig.  19)  serves 
to  show  that  it  may  sometimes  be  almost  as  short  in 
the  orang  as  it  normally  is  in  man — both  the  human 
subjects  of  this  illustration  having  been  normal. 

(7)  Ear. — Mr.  Darwin  writes : — 

The  celebrated  sculptor,  Mr.  Woolner,  informs  me  of  one 
little  peculiarity  in  the  external  ear,  which  he  has  often  observed 
both  in  men  and  women  ....  The 
peculiarity  consists  in  a  little  blunt 
point,  projecting  from  the  inwardly 
folded  margin,  or  helix.  When 
present,  it  is  developed  at  birth,  and, 
according  to  Prof.  Ludwig  Meyer, 
more  frequently  in  man  than  in 

M  JHl  yjJM  ^  Jr  woman-  Mr.  Woolner  made  an  exact 
If  \^$JiirSJr  model  of  one  such  case,  and  sent  me 
V  |\  ^"^^r  the  accompanying  drawing  ....  The 

\  \^^^^^  helix  obviously  consists  of  the  extreme 

^^^  margin   of  the   ear   folded  inwards ; 

and  the  folding  appears  to  be  in  some 
nr,.    20  —  Human    ear,  manner  connected  with  the  whole  ex- 
modelled  and  drawn  by  ,          ,    . 

Mr.    Woolner.      a,     the  tCrnal  Car  be'ng  Permanently  Passed 

projecting  point  backwards.     In  many  monkeys,  which 

do  not  stand  high   in  the  order,  as 

baboons  and  some  species  of  macacus,  the  upper  portion  of 
the  ear  is  slightly  pointed,  and  the  margin  is  not  at  all  folded 
inwards ;  but  if  the  margin  were  to  be  thus  folded,  a  slight 

point  would  necessarily  project  towards  the  centre The 

following  wood-cut  is  an  accurate  copy  of  a  photograph  of  the 
foetus  of  an  orang  (kindly  sent  me  by  Dr.  Nitsche),  in  which  it 
may  be  seen  how  different  the  pointed  outline  of  the  ear  is  at 
this  period  from  its  adult  condition,  when  it  bears  a  close 


Morphology.  87 

general  resemblance  to  that  of  man  [including  even  the  occa- 
sional appearance  of  the  projecting  point  shown  in  the  preceding 
woodcut].  It  is  evident  that  the  folding  over  of  the  tip  of  such 
an  ear,  unless  it  changed  greatly  during  its  further  development, 
would  give  rise  to  a  point  projecting  inwards '. 


FIG.  21. — Foetus  of  an  Orang.     Exact  copy  of  a  photograph, 
showing  the  form  of  the  e.n  at  this  early  stage. 

The  following  woodcut  serves  still  further  to  show 
vestigial  resemblances  between  the  human  ear  and 
that  of  apes.  The  last  two  figures  illustrate  the 
general  resemblance  between  the  normal  ear  of  foetal 
man  and  the  ear  of  an  adult  orang-outang.  The 
other  two  figures  on  the  lower  line  are  intended  to 
exhibit  occasional  modifications  of  the  adult  human 
ear,  which  approximate  simian  characters  somewhat 
more  closely  than  does  the  normal  type.  It  will  be 
observed  that  in  their  comparatively  small  lobes  these 
ears  resemble  those  of  all  the  apes  ;  and  that  while  the 
outer  margin  of  one  is  not  unlike  that  of  the  Barbary 

1  Descent  of  Man,  2nd  ed.,  pp.  15-16. 


Morphology.  89 

ape,  the  outer  margin  of  the  other  follows  those  of  the 
chimpanzee  and  orang.  Of  course  it  would  be  easy 
to  select  individual  human  ears  which  present  either 
of  these  characters  in  a  more  pronounced  degree ; 
but  these  ears  have  been  chosen  as  models  because 
they  present  both  characters  in  conjunction.  The 
upper  row  of  figures  likewise  shows  the  close  similarity 
of  hair-tracts,  and  the  direction  of  growth  on  the  part 
of  the  hair  itself,  in  cases  where  the  human  ear  happens 
to  be  of  an  abnormally  hirsute  character.  But  this 
particular  instance  (which  I  do  not  think  has  been 
previously  noticed)  introduces  us  to  the  subject  of  hair, 
and  hair-growth,  in  general. 

(8)  Hair.—  Adult  man  presents  rudimentary  hair 
over  most  parts  of  the  body.  Wallace  has  sought  to 
draw  a  refined  distinction  between  this  vestigial  coating 
and  the  useful  coating  of  quadrumanous  animals,  in 
the  absence  of  the  former  from  the  human  back.  But 
even  this  refined  distinction  does  not  hold.  On  the 
one  hand,  the  comparatively  hairless  chimpanzee 
which  died  last  year  in  the  Zoological  Gardens  (T. 
calvus]  was  remarkably  denuded  over  the  back  ;  and, 
on  the  other  hand,  men  who  present  a  considerable 
development  of  hair  over  the  rest  of  their  bodies 
present  it  also  on  their  backs  and  shoulders.  Again, 
in  all  men  the  rudimentary  hair  on  the  upper  and 
lower  arm  is  directed  towards  the  elbow — a  peculiarity 
which  occurs  nowhere  else  in  the  animal  kingdom, 
with  the  exception  of  the  anthropoid  apes  and  a  few 
American  monkeys,  where  it  presumably  has  to  do 
with  arboreal  habits.  For,  when  sitting  in  trees,  the 
orang,  as  observed  by  Mr.  Wallace,  places  its  hands 
above  its  head  with  its  elbows  pointing  downwards : 


FlG.  23. —  Hair-tracts  on  the  aims  and  hands  of  Man,  as  compared 
with  those  on  the  arms  and  hands  of  Chimpanzee.     Drawn  from  life. 


Morphology.  91 

the  disposition  of  hair  on  the  arms  and  fore-arms  then 
has  the  effect  of  thatch  in  turning  the  rain.  Again, 
I  find  that  in  all  species  of  apes,  monkeys,  and 
baboons  which  I  have  examined  (and  they  have  been 
numerous),  the  hair  on  the  backs  of  the  hands  and 
feet  is  continued  as  far  as  the  first  row  of  phalanges  ; 
but  becomes  scanty,  or  disappears  altogether,  on  the 
second  row ;  while  it  is  invariably  absent  on  the 
terminal  row.  I  also  find  that  the  same  peculiarity 
occurs  in  man.  We  all  have  rudimentary  hair  on  the 
first  row  of  phalanges,  both  of  hands  and  feet :  when 
present  at  all,  it  is  more  scanty  on  the  second  row ; 
and  in  no  case  have  I  been  able  to  find  any  on 
the  terminal  row.  In  all  cases  these  peculiarities  are 
congenital,  and  the  total  absence  or  partial  presence 
of  hair  on  the  second  phalanges  is  constant  in  different 
species  of  Quadrumana.  For  instance,  it  is  entirely 
absent  in  all  the  chimpanzees,  which  I  have  examined, 
while  scantily  present  in  all  the  orangs.  As  in  man, 
it  occurs  in  a  patch  midway  between  the  joints. 

Besides  showing  these  two  features  with  regard  to 
the  disposition  of  hair  on  the  human  arm  and  hand, 
the  above  woodcut  illustrates  a  third.  By  looking 
closely  at  the  arm  of  the  very  hniry  man  from  whom 
the  drawing  was  taken,  it  could  be  seen  that  there  was 
a  strong  tendency  towards  a  whorled  arrangement 
of  the  hairs  on  the  backs  of  the  wrists.  This  is 
likewise,  as  a  general  rule,  a  marked  feature  in  the 
arrangement  of  hair  on  the  same  places  in  the  gorilla, 
orang,  and  chimpanzee.  In  the  specimen  of  the 
latter,  however,  from  which  the  drawing  was  taken, 
this  characteristic  was  not  well  marked.  The  down- 
ward direction  of  the  hair  on  the  backs  of  the  hands 


92  Darwin,  and  after  Darwin. 

is  exactly  the  same  in  man  as  it  is  in  all  the  anthropoid 
apes.  Again,  with  regard  to  hair,  Darwin  notices  that 
occasionally  there  appears  in  man  a  few  hairs  in  the 
eyebrows  much  longer  than  the  others  ;  and  that  they 
seem  to  be  representative  of  similarly  long  and  scattered 
hairs  which  occur  in  the  chimpanzee,  macacus,  and 
baboons. 

Lastly,  it  may  be  here  more  conveniently  observed 
than  in  the  next  chapter  on  Embryology,  that  at 
about  the  sixth  month  the  human  foetus  is  often 
thickly  coated  with  somewhat  long  dark  hair  over 
the  entire  body,  except  the  soles  of  the  feet  and 
palms  of  the  hands,  which  are  likewise  bare  in  all 
quadrumanous  animals.  This  covering,  which  is  called 
the  lanugo,  and  sometimes  extends  even  to  the  whole 
forehead,  ears,  and  face,  is  shed  before  birth.  So  that 
it  appears  to  be  useless  for  any  purpose  other  than 
that  of  emphatically  declaring  man  a  child  of  the 
monkey. 

(9)  Teeth.—  Darwin  writes: — 

It  appears  as  if  the  posterior  molar  or  wisdom-teeth  were 
tending  to  become  rudimentary  in  the  more  civilized  races  of 
man.  These  teeth  are  rather  smaller  than  the  other  molars,  as 
is  likewise  the  case  with  the  corresponding  teeth  in  the  chim- 
panzee and  orang  ;  and  they  have  only  two  separate  fangs  .... 
They  are  also  much  more  liable  to  vary,  both  in  structure  and  in 
the  period  of  their  development,  than  the  other  teeth.  In  the 
Melanian  races,  on  the  other  hand,  the  wisdom-teeth  are  usually 
furnished  with  three  separate  fangs,  and  are  usually  sound  [i.e. 
not  specially  liable  to  decay]  ;  they  also  differ  from  the  other 
molars  in  size,  less  than  in  the  Caucasian  races. 

Now,  in  addition  to  these  there  are  other  respects 
in  which  the  dwindling  condition  of  wisdom-teeth  is 
manifested — particularly  with  regard  to  the  pattern  of 


Morphology. 


93 


their  crowns.  Indeed,  in  this  respect  it  would  seem 
that  even  in  the  anthropoid  apes  there  is  the  be- 
ginning of  a  tendency  to  degeneration  of  the  molai 
teeth  from  behind  forwards.  For  if  we  compare  the 
three  molars  in  the  lower  jaw  of  the  gorilla,  orang, 
and  chimpanzee,  we  find  that  the  gorilla  has  five  well- 


FIG.  24. — Molar  teeth   of  lower  jaw  in   Gorilla,   Orang,  and  Man. 
Drawn  from  nature,  nat.  size  (A".  A/us.  Coll.  Surg.}. 

marked  cusps  on  all  three  of  them  ;  but  that  in  the 
orang  the  cusps  are  not  so  pronounced,  while  in  the 
chimpanzee  there  are  only  four  of  them  on  the  third 
molar.  Now  in  man  it  is  only  the  first  of  these  three 
teeth  which  normally  presents  five  cusps,  both  the 
others  presenting  only  four.  So  that,  comparing  all 


94  Darwin,  and  after  Darwin. 

these  genera  together,  it  appears  that  the  numbei 
of  cusps  is  being  reduced  from  behind  forwards ; 
the  chimpanzee  having  lost  one  of  them  from  the 
third  molar,  while  man  has  not  only  lost  this,  but 
also  one  from  the  second  molar, — and,  it  may  be  added, 
likewise  partially  (or  even  totally)  from  the  first  molar, 
as  a  frequent  variation  among  civilized  races.  But,  on 
the  other  hand,  variations  are  often  met  with  in  the 
opposite  direction,  where  the  second  or  the  third 
molar  of  man  presents  five  cusps — in  the  one  case 
following  the  chimpanzee,  in  the  other  the  gorilla. 
These  latter  variations,  therefore,  may  fairly  be  re- 
garded as  reversionary.  For  these  facts  I  am  indebted 
to  the  kindness  of  Mr.  C.  S.  Tomes. 

(10)  Perforations  of  the  humerus. — The  peculiarities 
which  we  have  to  notice  under  this  heading  are  two  in 
number.  First,  the  supra-  condyloid  foramen  is  a  nor- 
mal feature  in  some  of  the  lower  Quadrumana  (Fig.  25), 
where  it  gives  passage  to  the  great  nerve  of  the  fore- 
arm, and  often  also  to  the  great  artery.  In  man,  how- 
ever, it  is  not  a  normal  feature.  Yet  it  occurs  in  a 
small  percentage  of  cases — viz.,  according  to  Sir  W. 
Turner,  in  about  one  per  cent.,  and  therefore  is  regarded 
by  Darwin  as  a  vestigial  character.  Secondly,  there  is 
inter-condyloid  foramen,  which  is  also  situated  near 
the  lower  end  of  the  humerus,  but  more  in  the  middle 
of  the  bone.  This  occurs,  but  not  constantly,  in  apes, 
and  also  in  the  human  species.  From  the  fact  that  it 
does  so  much  more  frequently  in  the  bones  of  ancient — 
and  also  of  some  savage — races  of  mankind  (viz.  in  20 
to  30  per  cent,  of  cases),  Darwin  is  disposed  to  regard 
it  also  as  a  vestigial  feature.  On  the  other  hand,  Prof. 
Flower  tells  me  that  in  his  opinion  it  is  but  an  ex- 


Morphology. 


95 


pression  of  impoverished  nutrition  during  the  growth 
of  the  bone. 


|       JAVA!/  LOR.IS. 


GAPVCHII/. 


FIG.  25. — Perforation  of  the  humerus  (supra-condyloid  foramen)  in 
three  species  of  Quadrumana  where  it  normally  occurs,  and  in  Man,  where 
it  does  not  normally  occur.  Drawn  from  nature  (A'.  Coll.  Snrg.  Mus.). 

(n)  Flattening  of  tibia. — In  some  very  ancient 
human  skeletons,  there  has  also  been  found  a  lateral 
flattening  of  the  tibia,  which  rarely  occurs  in  any  ex- 
isting human  beings,  but  which  appears  to  have  been 
usual  among  the  earliest  races  of  mankind  hitherto  dis- 
covered. According  to  Broca,  the  measurements  of 
these  fossil  human  tibiae  resemble  those  of  apes.  More- 
over, the  bone  is  bent  and  strongly  convex  forwards, 
while  its  angles  are  so  rounded  as  to  present  the 
nearly  oval  section  seen  in  apes.  It  is  in  association 
with  these  ape-like  human  tibiae  That  perforated  humeri 
of  man  are  found  in  greatest  abundance. 


96  Darwin,  and  after  Darwin. 

On  the  other  hand,  however,  there  is  reason  to  doubt 
whether  this  form  of  tibia  in  man  is  really  a  survival 
from  his  quadrumanous  ancestry.  For,  as  Boyd- 
Dawkins  and  Hartmann  have  pointed  out,  the  degree 
of  flattening  presented  by  some  of  these  ancient 
human  bones  is  greater  than  that  which  occurs  in  any 
existing  species  of  anthropoid  ape.  Of  course  the 
possibility  remains  that  the  unknown  species  of  ape 
from  which  man  descended  may  have  had  its  tibia 
more  flattened  than  is  now  observable  in  any  of  the 
existing  species.  Nevertheless,  as  some  doubt  attaches 
to  this  particular  case,  I  do  not  press  it — and,  indeed, 
only  mention  it  at  all. in  order  that  the  doubt  may  be 
expressed. 

Similarly,  I  will  conclude  by  remarking  that  several 
other  instances  of  the  survival  of  vestigial  structures 
in  man  have  been  alleged,  which  are  of  a  still  more 
doubtful  character.  Of  such,  for  example,  are  the 
supposed  absence  of  the  genial  tubercle  in  the  case 
of  a  very  ancient  jaw-bone  of  man  and  the  disposition 
of  valves  in  human  veins.  From  the  former  it  was 
argued  that  the  possessor  of  this  very  ancient  jaw-bone 
was  probably  speechless,  inasmuch  as  the  tubercle  in 
existing  man  gives  attachment  to  muscles  of  the 
tongue.  From  the  latter  it  has  been  argued  that  all 
the  valves  in  the  veins  of  the  human  body  have 
reference,  in  their  disposition,  to  the  incidence  of  blood- 
pressure  when  the  attitude  of  the  body  is  horizontal, 
or  quadrupedal.  Now,  the  former  case  has  already 
broken  down,  and  I  find  that  the  latter  does  not  hold. 
But  we  can  well  afford  to  lose  such  doubtful  and 
spurious  cases,  in  view  of  all  the  foregoing  unquestion- 
able and  genuine  cases  of  vestigial  structures  which  are 


Morphology.  97 

to  be  met  with  even  within  the  limits  of  our  own 
organization — and  even  when  these  limits  are  still 
further  limited  by  selecting  only  those  instances  which 
refer  to  the  very  latest  chapter  of  our  long  ancestral 
history. 


CHAPTER  IV. 

EMBRYOLOGY. 

WE  will  next  consider  what  of  late  years  has 
become  the  most  important  of  the  lines  of  evidence. 
not  only  in  favour  of  the  general  fact  of  evolution, 
but  also  of  its  history  :  I  mean  the  evidence  which  has 
been  yielded  by  the  newest  of  the  sciences,  the  science 
of  Embryology.  But  here,  as  in  the  analogous  case 
of  adult  morphology,  in  order  to  do  justice  to  the 
mass  of  evidence  which  has  now  been  accumulated. 
a  whole  volume  would  be  necessary.  As  in  that 
previous  case,  therefore,  I  must  restrict  myself  to 
giving  an  outline  sketch  of  the  main  facts. 

First  I  will  display  what  in  the  language  of  Paley 
we  may  call  "  the  state  of  the  argument." 

It  is  an  observable  fact  that  there  is  often  a  close 
correspondence  between  developmental  changes  as 
revealed  by  any  chronological  series  of  fossils  which 
may  happen  to  have  been  preserved,  and  develop- 
mental changes  which  may  be  observed  during  the 
life-history  of  now  existing  individuals  belonging  to 
the  same  group  of  animals.  For  instance,  the 
successive  development  of  prongs  in  the  horns  of 
deer-like  animals,  which  is  so  clearly  shown  in  the 
geological  history  of  this  l:ibe,  is  closely  reproduced 


Embryology.  99 

in  the  life-history  of  existing  deer.  Or,  in  other 
words,  the  antlers  of  an  existing  deer  furnish  in  their 
development  a  kind  of  re'sume',  or  recapitulation,  of  the 
successive  phases  whereby  the  primitive  horn  was  grad- 
ually superseded  by  horns  presenting  a  greater  and 
greater  numberof  prongs  in  successive  species  of  extinct 
deer  (Fig.  26).  Now  it  must  be  obvious  that  such  a  re- 
capitulation in  the  life-history  of  an  existing  animal  of 
developmental  changes  successively  distinctive  of  sundry 
allied,  though  now  extinct  species,  speaks  strongly  in 
favour  of  evolution.  For  as  it  is  of  the  essence  of  this 
theory  that  new  forms  arise  from  older  forms  by  way 
of  hereditary  descent,  we  should  antecedently  expect, 
if  the  theory  is  true,  that  the  phases  of  development 
presented  by  the  individual  organism  would  follow,  in 
their  main  outlines,  those  phases  of  development 
through  which  their  long  line  of  ancestors  had  passed. 
The  only  alternative  view  is  that  as  species  of  deer, 
for  instance,  were  separately  created,  additional  prongs 
were  successively  added  to  their  antlers  ;  and  yet 
that,  in  order  to  be  so  added  to  successive  species, 
every  individual  deer  belonging  to  later  species  was 
required  to  repeat  in  his  own  lifetime  the  process  of 
successive  additions  which  had  previously  taken 
place  in  a  remote  series  of  extinct  species.  Now  I 
do  not  deny  that  this  view  is  a  possible  view ;  but  I 
do  deny  that  it  is  a  probable  one.  According  to 
the  evolutionary  interpretation  of  such  facts,  we  can 
see  a  very  good  reason  why  the  life-history  of  the 
individual  is  thus  a  condensed  re'sumt  of  the  life- 
history  of  its  ancestral  species.  But  according  to  the 
opposite  view  no  reason  can  be  assigned  why  such 
should  be  the  case.  In  a  previous  chapter — the 
H  2 


FlG.  26.  —  Antlers  of  Stag,  showing  successive  addition  of  branch 
Drawn  from  nature  (Brit.  A/z«.)- 


in  successiv 


Em  b  ryology.  i  o  I 

chapter  on  Classification — we  have  seen  that  if  each 
species  were  created  separately,  no  reason  can  be 
assigned  why  they  should  all  have  been  turned  out 
upon  structural  patterns  so  strongly  suggestive  of 
hereditary  descent  with  gradual  modifications,  or  slow 
divergence — the  result  being  group  subordinated  to 
group,  with  the  most  generalized  (or  least  developed) 
forms  at  the  bottom,  and  the  highest  products  of 
organization  at  the  top.  And  now  we  see — or  shall 
immediately  see — that  this  consideration  admits  of 
being  greatly  fortified  by  a  study  of  the  develop- 
mental history  of  every  individual  organism.  If  it 
would  be  an  unaccountable  fact  that  every  separately 
created  species  should  have  been  created  with  close 
structural  resemblances  to  a  certain  limited  number 
of  other  species,  less  close  resemblances  to  certain 
further  species,  and  so  backwards  ;  assuredly  it  would 
be  a  still  more  unaccountable  fact  that  every  indi- 
vidual of  every  species  should  exhibit  in  its  own 
person  a  history  of  developmental  change,  every  term 
of  which  corresponds  with  the  structural  peculiarities 
of  its  now  extinct  predecessors — and  this  in  the  exact 
historical  order  of  their  succession  in  geological  time. 
The  more  that  we  think  about  this  antithesis  between 
the  naturalistic  and  the  non-naturalistic  interpreta- 
tions, the  greater  must  we  feel  the  contrast  in  respect 
of  rationality  to  become ;  and,  therefore,  I  need  not 
spend  time  by  saying  anything  further  upon  the 
antecedent  standing  of  the  two  theories  in  this 
respect.  The  evidence,  then,  which  I  am  about  to 
adduce  from  the  study  of  development  in  the  life- 
histories  of  individual  organisms,  will  be  regarded  by 
me  as  so  much  unquestionable  evidence  in  favour  of 


IO2          Darwin,  and  after  Darwin. 

similar  processes  of  development  in  the  life-histories 
of  their  respective  species— in  so  far,  I  mean,  as  the 
two  sets  of  changes  admit  of  being  proved  parallel. 

In  the  only  illustration  hitherto  adduced — viz.  that 
of  deers'  horns — the  series  of  changes  from  a  one- 
pronged  horn  to  a  fully  developed  arborescent  antler, 
is  a  series  which  takes  place  during  the  adult  life  of 
the  animal ;  for  it  is  only  when  the  breeding  age 
has  been  attained  that  horns  are  required  to  appear. 
But  seeing  that  every  animal  passes  through  most  of 
the  phases  of  its  development,  not  only  before  the 
breeding  age  has  been  attained,  but  even  before  the 
time  of  its  own  birth,  clearly  the  largest  field  for 
the  study  of  individual  development  is  furnished  by 
embryology.  For  instance,  there  is  a  salamander 
which  differs  from  most  other  salamanders  in  being 
exclusively  terrestrial  in  its  habits.  Now,  the  young 
of  this  salamander  before  their  birth  are  found  to 
be  furnished  with  gills,  which,  however,  they  are  never 
destined  to  use.  Yet  these  gills  are  so  perfectly 
formed,  that  if  the  young  salamanders  be  removed 
from  the  body  of  their  mother  shortly  before  birth, 
and  be  then  immediately  placed  in  water,  the 
little  animals  show  themselves  quite  capable  of 
aquatic  respiration,  and  will  merrily  swim  about  in 
a  medium  which  would  quickly  drown  their  own 
parent.  Here,  then,  we  have  both  morphological  and 
physiological  evidence  pointing  to  the  possession  of 
gills  by  the  ancestors  of  the  land  salamander. 

It  would  be  easy  to  devote  the  whole  of  the  present 
chapter  to  an  enumeration  of  special  instances  of  the 
kinds  thus  chosen  for  purposes  of  illustration ;  but 
as  it  is  desirable  to  take  a  deeper,  and  therefore 


Embryology.  103 

a  more  general  view  of  the  whole  subject,  I  will  begin 
at  the  foundation,  and  gradually  work  up  from  the 
earliest  stages  of  development  to  the  latest.  Before 
starting,  however,  I  ask  the  reader  to  bear  in  mind 
one  consideration,  which  must  reasonably  prevent 
our  anticipating  that  in  every  case  the  life-history  of 
an  individual  organism  should  present  a  /^//recapitu- 
lation of  the  life-history  of  its  ancestral  line  of  species. 
Supposing  the  theory  of  evolution  to  be  true,  it  must 
follow  that  in  many  cases  it  would  have  been  more  or 
less  disadvantageous  to  a  developing  type  that  it 
should  have  been  obliged  to  reproduce  in  its  individual 
representatives  all  the  phases  of  development  pre- 
viously undergone  by  its  ancestry — even  within  the 
limits  of  the  same  family.  We  can  easily  understand, 
for  example,  that  the  waste  of  material  required  for 
building  up  the  useless  gills  of  the  embryonic  sala- 
manders is  a  waste  which,  sooner  or  later,  is  l-ikely  to 
be  done  away  with  ;  so  that  the  fact  of  its  occurring 
at  all  is  in  itself  enough  to  show  that  the  change  from 
aquatic  to  terrestrial  habits  on  the  part  of  this  species 
must  have  been  one  of  comparatively  recent  occurrence. 
Now,  in  as  far  as  it  is  detrimental  to  a  developing 
type  that  it  should  pass  through  any  particular  ances- 
tral phases  of  development,  we  may  be  sure  that  natural 
selection — or  whatever  other  adjustive  causes  we  may 
suppose  to  have  been  at  work  in  the  adaptation  of 
organisms  to  their  surroundings — will  constantly  seek 
to  get  rid  of  this  necessity,  with  the  result,  when 
successful,  of  dropping  out  the  detrimental  phases. 
Thus  the  foreshortening  of  developmental  history 
which  takes  place  in  the  individual  lifetime  may  be 
expected  often  to  take  place,  not  only  in  the  way  of 


IO4          Darwin,  and  after  Darwin. 

condensation,  but  also  in  the  way  of  excision.  Many 
pages  of  ancestral  history  may  be  recapitulated  in 
the  paragraphs  of  embryonic  development,  while 
others  may  not  be  so  much  as  mentioned.  And  that 
this  is  the  true  explanation  of  what  embryologists 
term  "  direct "  development — or  of  a  more  or  less 
sudden  leap  from  one  phase  to  another,  without  any 
appearance  of  intermediate  phases — is  proved  by  the 
fact  that  in  some  cases  both  direct  and  indirect  develop- 
ment occur  within  the  same  group  of  organisms,  some 
genera  or  families  having  dropped  out  the  intermediate 
phases  which  other  genera  or  families  retain. 

The  argument  from  embryology  must  be  taken  to 
begin  with  the  first  beginning  of  individual  life  in  the 
ovum.  And,  in  order  to  understand  the  bearings  of 
the  argument  in  this  its  first  stage,  we  must  consider 
the  phenomena  of  reproduction  in  the  simplest  form 
which  these  phenomena  are  known  to  present. 

The  whole  of  the  animal  kingdom  is  divided  into 
two  great  groups,  which  are  called  the  Protozoa  and 
the  Metazoa.  Similarly,  the  whole  of  the  vegetable 
kingdom  is  divided  into  the  Protophyta  and  the  Meta- 
phyta.  The  characteristic  feature  of  all  the  Protozoa 
and  Protophyta  is  that  the  organism  consists  of  a 
single  physiological  cell,  while  the  characteristic  of  all 
the  Metazoa  and  Metaphyta  is  that  the  organism 
consists  of  a  plurality  of  physiological  cells,  variously 
modified  to  subserve  different  functions  in  the 
economy  of  the  animal  or  plant,  as  the  case  may  be. 
For  the  sake  of  brevity,  I  shall  hereafter  deal  only 
with  the  case  of  animals  (Protozoa  and  Metazoa) ;  but 
it  may  throughout  be  understood  that  everything 


Embryology.  105 

which  is  said  applies  also  to  the  case  of  plants 
(Protophyta  and  Metaphyta). 

A  Protozoon  (like  a  Protophyton)  is  a  solitary  cell, 
or  a  "unicellular  organism,"  while  a  Metazoon  (like  a 
Metaphyton)  is  a  society  of  cells,  or  a  "  multicellular 
organism."  Now,  it  is  only  in  the  multicellular 
organisms  that  there  is  any  observable  distinction  of 
sex.  In  all  the  unicellular  organisms  the  phenomena 
of  reproduction  appear  to  be  more  or  less  identical 
with  those  of  growth.  Nevertheless,  as  these  phe- 
nomena are  here  in  some  cases  suggestively  peculiar, 
I  will  consider  them  more  in  detail. 

A  Protozoon  is  a  single  corpuscle  of  protoplasm, 
which  in  different  species  of  Protozoa  varies  in  size 
from  more  than  one  inch  to  less  than  ^V^  °f  an  mch 
in  diameter.  In  some  species  there  is  an  enveloping 
cortical  substance ;  in  other  species  no  such  substance 
can  be  detected.  Again,  in  most  species  there  is  a 
nucleus,  while  in  other  species  no  such  differentiation 
of  structure  has  hitherto  been  observed.  Nevertheless, 
from  the  fact  that  the  nucleus  occurs  in  the  majority 
of  Protozoa,  coupled  with  the  fact  that  the  demon- 
stration of  this  body  is  often  a  matter  of  extreme 
difficulty,  not  only  in  some  of  the  Protozoa  where  it 
has  been  but  recently  detected,  but  also  in  the  case  of 
certain  physiological  cells  elsewhere, — fror  these  facts 
it  is  not  unreasonable  to  suppose  that  all  the  Protozoa 
possess  a  nucleus,  whether  or  not  it  admits  of  being 
rendered  visible  by  histological  methods  thus  far  at 
our  disposal.  If  this  is  the  case,  we  should  be  justi- 
fied in  saying,  as  I  have  said,  that  a  Protozoon  is  an 
isolated  physiological  cell,  and,  like  cells  in  general, 
multiplies  by  means  of  what  Spencer  and  Hackel 


IO6  Darwin,  and  after  Darwin. 

have  aptly  called  a  process  of  discontinuous  growth. 
That  is  to  say,  when  a  cell  reaches  maturity,  further 
growth  takes  place  in  the  direction  of  a  severance  of 
its  substance -the  separated  portion  thus  starting 
anew  as  a  distinct  physiological  unit.  But,  notwith- 
standing the  complex  changes  which  have  been  more 
recently  observed  to  take  place  in  the  nucleus  of  some 
Protozoa  prior  to  their  division,  the  process  of 
multiplication  by  division  may  still  be  regarded  as  a 
process  of  growth,  which  differs  from  the  previous 
growth  of  the  individual  cell  in  being  attended  by  a 
severance  of  continuity.  If  we  take  a  suspended  drop 
of  gum,  and  gradually  add  to  its  size  by  allowing 
more  and  more  gum  to  flow  into  it,  a  point  will 
eventually  be  reached  at  which  the  force  of  gravity 
will  overcome  that  of  cohesion,  and  a  portion  of  the 
drop  will  fall  away  from  the  remainder.  Here  we 
have  a  rough  physical  simile,  although  of  course  no 
true  analogy.  In  virtue  of  a  continuous  assimilation 
of  nutriment,  the  protoplasm  of  a  cell  increases  in 
mass,  until  it  reaches  the  size  at  which  the  forces  of 
disruption  overcome  those  of  cohesion — or,  in  other 
words,  the  point  at  which  increase  of  size  is  no  longer 
compatible  with  continuity  of  substance.  Neverthe- 
less, it  must  not  be  supposed  that  the  process  is  thus 
merely  a  physical  one.  The  phenomena  which  occur 
even  in  the  simplest— or  so-called  "direct" — cell- 
division,  are  of  themselves  enough  to  prove  that  the 
process  is  vital,  or  physiological ;  and  this  in  a  high 
degree  of  specialization.  But  so,  likewise,  are  all 
processes  of  growth  in  organic  structures  ;  and  there- 
fore the  simile  of  the  drop  of  gum  is  not  to  be 
regarded  as  a  true  analogy :  it  serves  only  to 


Embryology. 


107 


indicate  the  fact  that  when  cell-growth  proceeds 
beyond  a  certain  point  cell-division  ensues.  The 
size  to  which  cells  may  grow  before  they  thus  divide 
is  very  variable  in  different  kinds  of  cells  ;  for  while 
some  may  normally  attain  a  length  of  ten  or  twelve 
inches,  others  divide  before  they  measure  yoVtr  °f  an 
inch.  This,  however,  is  a  matter  of  detail,  and  does 
not  affect  the  general  physiological  principles  on 
which  we  are  at  present  engaged. 


FIG.  27. — Fission  of  a  Protozoon.  In  the  left-hand  drawing  the  process 
is  represented  as  having  advanced  sufficiently  far  to  have  caused  a 
division  and  segregation  both  of  the  nucleus  and  the  vesicle.  In  the 
right-hand  drawing  the  process  is  represented  as  complete,  n,  N, 
severed  nucleus ;  vc ,  severed  vesicle ;  fs,  pseudopodia ;/,  ingested  food. 

Now,  as  we  have  seen,  a  Protozoon  is  a  single  cell ; 
for  even  although  in  some  of  the  higher  forms  of 
protozoal  life  a  colony  of  cells  may  be  bound  together 
in  organic  connexion,  each  of  these  cells  is  in  itself  an 
"  individual,"  capable  of  self-nourishment,  reproduction, 
and,  generally,  of  independent  existence.  Conse- 
quently, when  the  growth  of  a  Protozoon  ends  in  a 
division  of  its  substance,  the  two  parts  wander  away 
from  each  other  as  separate  organisms.  (Fig.  27.) 


io8          Darwin,  and  after  Darwin. 

The  next  point  we  have  to  observe  is,  that  in  all 
cases  where  a  cell  or  a  Protozoon  multiplies  by 
way  of  fissiparous  division,  the  process  begins  in  the 
nucleus.  If  the  nucleus  divides  into  two  parts,  the 
whole  cell  will  eventually  divide  into  two  parts,  each 
of  which  retains  a  portion  of  the  original  nucleus,  as 
represented  in  the  above  figure.  If  the  nucleus  divides 
into  three,  four,  or  even,  as  happens  in  the  develop- 
ment of  some  embryonic  tissues,  into  as  many  as  six 
parts,  the  cell  will  subdivide  into  a  corresponding 
number,  each  retaining  a  portion  of  the  nucleus. 
Therefore,  in  all  cases  of  fissiparous  division,  the 
seat  or  origin  of  the  process  is  the  nucleus. 

Thus  far,  then,  the  phenomena  of  multiplication  are 
identical  in  all  the  lowest  or  unicellular  organisms, 
and  in  the  constituent  cells  of  all  the  higher  or  multi- 
cellular.  And  this  is  the  first  point  which  I  desire  to 
make  apparent.  For  where  the  object  is  to  prove  a 
continuity  between  the  phenomena  of  growth  and 
reproduction,  it  is  of  primary  importance  to  show — 
ist,  that  there  is  such  a  continuity  in  the  case  of  all 
the  unicellular  organisms,  and,  2nd,  that  there  are  all 
the  above  points  of  resemblance  between  the  multi- 
plication of  cells  in  the  unicellular  and  in  the  multi- 
cellular  organisms. 

It  remains  to  consider  the  points  of  difference,  and, 
if  possible,  to  show  that  these  do  not  go  to  disprove 
the  doctrine  of  continuity  which  the  points  of  resem- 
blance so  forcibly  indicate. 

The  first  point  of  difference  obviously  is,  that  in  the 
case  of  all  the  multicellular  organisms  the  two  or 
more  "  daughter- cells,"  which  are  produced  by  division 
of  the  "  mother-cell,"  do  not  wander  away  from  one 


Embryology.  109 

another ;  but,  as  a  rule,  they  continue  to  be  held  in  more 
or  less  close  apposition  by  means  of  other  cells  and 
binding  membranes, — with  the  result  of  giving  rise  to 
those  various  c;  tissues,"  which  in  turn  go  to  constitute 
the  material  of  "  organs."  I  cannot  suppose,  however, 
that  any  advocate  of  discontinuity  will  care  to  take 
his  stand  at  this  point.  But,  if  any  one  were  so 
foolish  as  to  do  so,  it  would  be  easy  to  dislodge  him 
by  describing  the  state  of  matters  in  some  of  the 
Protozoa  where  a  number  of  unicellular  "  individuals  " 
are  organically  united  so  as  to  form  a  "  colony." 
These  cases  serve  to  bridge  this  distinction  between 
Protozoa  and  Metazoa,  of  which  therefore  we  may 
now  take  leave. 

In  the  second  place,  there  is  the  no  less  obvious 
distinction  that  the  result  of  cell-division  in  the 
Metazoa  is  not  merely  to  multiply  cells  all  of  the 
same  kind  :  on  the  contrary,  the  process  here  gives 
rise  to  as  many  different  kinds  of  cells  as  there  are 
different  kinds  of  tissue  composing  the  adult  organism. 
But  no  one,  I  should  think,  is  likely  to  oppose  the 
doctrine  of  continuity  on  the  ground  of  this  distinc- 
tion. For  the  distinction  is  clearly  one  which  must 
necessarily  arise,  if  the  doctrine  of  continuity  between 
unicellular  and  multicellular  organisms  be  true.  In 
other  words,  it  is  a  distinction  which  the  theory  of 
evolution  itself  must  necessarily  pre-suppose,  and 
therefore  it  is  no  objection  to  the  theory  that  its 
pre-supposition  is  realized.  Moreover,  as  we  shall 
see  better  presently,  there  is  no  difficulty  in  under- 
standing why  this  distinction  should  have  arisen,  so 
soon  as  it  became  necessary  (or  desirable)  that  indi- 
vidual cells,  when  composing  a  "  colony,"  should 


no          Darwin,  and  after  Farwin. 

conform  to  the  economic  principle  of  the  division  of 
labour— a  principle,  indeed,  which  is  already  fore- 
shadowed in  the  constituent  parts  of  a  single  cell, 
since  the  nucleus  has  one  set  of  functions  and  its 
surrounding  protoplasm  another. 

But  now,  in  the  third  place,  we  arrive  at  a  more 
important  distinction,  and  one  which  lies  at  the  root 
of  the  others  still  remaining  to  be  considered.  I  refer 
to  sexual  propagation.  For  it  is  a  peculiarity  of  the 
multicellular  organisms  that,  although  many  of  them 
may  likewise  propagate  themselves  by  other  means 
(Fig.  28),  they  all  propagate  themselves  by  means 
of  sexual  congress.  Now,  in  its  essence,  sexual  con- 
gress consists  in  the  fusion  of  two  specialized  cells 
(or,  as  now  seems  almost  certain,  of  the  nuclei  thereof), 
so  that  it  is  out  of  such  a  combination  that  the  new 
individual  arises  by  means  of  successive  cell-divisions, 
which,  beginning  in  the  fertilized  ovum,  eventually 
build  up  all  the  tissues  and  organs  of  the  body. 

This  process  clearly  indicates  very  high  specializa- 
tion on  the  part  of  germ-cells.  For  we  see  by  it  that 
although  these  cells  when  young  resemble  all  other 
cells  in  being  capable  of  self-multiplication  by  binary 
division  (thus  reproducing  cells  exactly  like  them- 
selves), when  older  they  lose  this  power ;  but,  at 
the  same  time,  they  acquire  an  entirely  new  and  very 
remarkable  power  of  giving  rise  to  a  vast  succession 
of  many  different  kinds  of  cells,  all  of  which  are 
mutually  correlated  as  to  their  several  functions,  so 
as  to  constitute  a  hierarchy  of  cells— or,  to  speak 
literally,  a  multicellular  co-organisation.  Here  it  is 
that  we  touch  the  really  important  distinction  between 
the  Protozoa  and  the  Metazoa  ;  for  although  I  have 


Embryology. 


ill 


said  that  some  of  the  higher  Protozoa  foreshadow  this 
state  of  matters  in  forming  cell-colonies,  it  must  now 
be  noted  that  the  cells  composing  such  colonies  are 
all  of  the  same  kind  ;  and,  therefore,  that  the  principle 


FIG.  28. — Hydra  iiridis,  partly  in  section.  M,  mouth;  O,  ovary,  or 
bud  containing  female  reproductive  cells ;  T,  testis,  or  bud  containing 
male  reproductive  cells.  In  addition  to  these  buds  containing  ger- 
minal elements  alone,  there  is  another  which  illustrates  the  process  of 
"  gemmation  " — i.  e.  the  direct  out-growth  of  a  fully  formed  offspring. 

of  producing  different  kinds  of  cells  which,  by  mutual 
co-adaptation  of  functions,  shall  be  capable  of  con- 
structing a  multiccllular  Metaxoon, — this  great  principle 
of  co- organization  is  but  dimly  nascent  in  the  cell- 


1 1 2  Darwin,  and  after  Larwin. 

colonies  of  Protozoa.  And  its  marvellous  development 
in  the  Metazoa  appears  ultimately  to  depend  upon  the 
highly  specialized  character  of  germ-cells.  Even  in 
cases  where  multicellular  organisms  are  capable  of  re- 
producing their  kind  without  the  need  of  any  preceding 
process  of  fertilization  (parthenogenesis),  and  even  in 
the  still  more  numerous  cases  where  complete  or- 
ganisms are  budded  forth  from  any  part  of  their  parent 
organism  (gemmation,  Fig.  28),  there  is  now  very  good 
reason  to  conclude  that  these  powers  of  a-sexual 
reproduction  on  the  part  of  multicellular  organisms 
are  all  ultimately  due  to  the  specialized  character  of 
their  germ-cells.  For  in  all  these  cases  the  tissues  of 
the  parent,  from  which  the  budding  takes  place,  were 
ultimately  derived  from  germ-cells — no  matter  how 
many  generations  of  budded  organisms  may  have 
intervened.  And  that  propagation  by  budding,  &c., 
in  multicellular  organisms  is  thus  ultimately  due  to 
their  propagation  by  sexual  methods,  seems  to  be 
further  shown  by  certain  facts  which  will  have  to  be 
discussed  at  some  length  in  my  next  volume.  Here, 
therefore,  I  will  mention  only  one  of  them — and  this 
because  it  furnishes  what  appears  to  be  another 
important  distinction  between  the  Protozoa  and  the 
Metazoa. 

In  nearly  all  cases  where  a  Protozoon  multiplies 
itself  by  fission,  the  process  begins  by  a  simple 
division  of  the  nucleus.  But  when  a  Metazoon  is  de- 
veloped from  a  germ-cell,  although  the  process  likewise 
begins  by  a  division  of  the  nucleus,  this  division  is  not 
a  simple  or  direct  one  ;  on  the  contrary,  it  is  inaugurated 
by  a  series  of  processes  going  on  within  the  nucleus, 
which  are  so  enormously  complex,  and  withal  so 


Embryology.  113 

beautifully  ordered  that  to  my  mind  they  constitute 
the  most  wonderful — if  not  also  the  most  suggestive 
— which  have  ever  been  revealed  by  microscopical  re- 
search. It  is  needless  to  say  that  I  refer  to  the 
phenomena  of  karyokinesis.  A  few  pages  further  on 
they  will  be  described  more  fully.  For  our  present 
purposes  it  is  sufficient  to  give  merely  a  pictorial 


FIG.  29. — Successive  stages  in  the  division  of  the  ovum,  or  egg-cell,  of 
a  worm.  (After  Strasburger.)  a  to  d  show  the  changes  taking  place  in 
the  nucleus  and  surrounding  cell- contents,  which  result  in  the  first 
segmentation  of  the  ovum  at  e :  f  and  g  show  a  repetition  of  these 
changes  in  each  of  the  two  resulting  cells,  leading  to  the  second  seg- 
mentation stage  at  h. 

illustration  of  their  successive  phases  ;  for  a  glance  at 
such  a  representation  serves  to  reveal  the  only  point  to 
which  attention  has  now  to  be  drawn — namely,  the 
immense  complexity  of  the  processes  in  question,  and 
therefore  the  contrast  which  they  furnish  to  the  simple 
(or  "  direct ")  division  of  the  nucleus  preparatory  to 
cell  division  in  the  unicellular  organisms.  Here,  then 
*  I 


H4          Darwin,  and  after  Darwin. 

(Fig.  29),  we  see  the  complex  processes  of  karyokinesis 
in  the  first  two  stages  of  egg-cell  division.  But 
similar  processes  continue  to  repeat  themselves  in 
subsequent  stages ;  and  this,  there  is  now  good  reason 
to  believe,  throughout  all  the  stages  of  cell-division, 
whereby  the  original  egg-cell  eventually  constructs  an 
entire  organism  In  other  words,  all  the  cells  com- 
posing all  the  tissues  of  a  multicellular  organism,  at 
all  stages  of  its  development,  are  probably  originated 
by  these  complex  processes,  which  differ  so  much 
from  the  simple  process  of  direct  division  in  the 
unicellular  organisms1.  In  this  important  respect, 
therefore,  it  does  at  first  sight  appear  that  we  have  a 
distinction  between  the  Protozoa  and  the  Metazoa  of 
so  pronounced  a  character,  as  fairly  to  raise  the 
question  whether  cell-division  is  fundamentally  identical 
in  unicellular  and  in  multicellular  organisms. 

Lastly,  the  only  other  distinction  of  a  physiologically 
significant  kind  between  a  single  cell  when  it  occurs 
as  a  Protozoon  and  when  it  does  so  as  the  unfertilized 
ovum  of  a  Metazoon  is,  that  in  the  latter  case  the 
nucleus  discharges  from  its  own  substance  two  minute 
protoplasmic  masses  ("  polar  bodies  "),  which  are  then 
eliminated  from  the  cell  altogether.  This  process, 
which  will  be  more  fully  described  later  on,  appears 
to  be  of  invariable  occurrence  in  the  case  of  all  egg-cells, 

1  I  say  "probably,"  because  analogy  points  in  this  direction.  As  a 
matter  of  fact,  in  many  cases  of  tissue-formation  karyokinesis  has  not 
hitherto  been  detected.  But  even  if  in  such  cases  it  does  not  occur — 
i.  e.  if  failure  to  detect  its  occurrence  be  not  due  merely  to  still  remain- 
ing imperfections  of  our  histological  methods, — the  large  number  of 
cases  in  which  it  has  been  seen  to  occur  in  the  formation  of  sundry 
tissues  are  of  themselves  sufficient  to  indicate  some  important  difference 
between  cells  derived  from  ova  (metazoal),  and  cells  which  have  not 
been  so  derived  (protozoal).  Which  is  the  point  now  under  discussion. 


Embryology.  115 

while  nothing  resembling  it  has  ever  been  observed  in 
any  of  the  Protozoa. 

We  must  now  consider  these  several  points  of 
difference  seriatim. 

First,  with  regard  to  sexual  propagation,  we  have 
already  seen  that  this  is  by  no  means  the  only  method 
of  propagation  among  the  multicellular  organisms  ; 
and  it  now  remains  to  add  that,  on  the  other  hand, 
there  is,  to  say  the  least,  a  suggestive  foreshadowing 
of  sexual  propagation  among  the  unicellular  organisms. 
For  although  simple  binary  fission  is  here  the  more 
usual  mode  of  multiplication,  very  frequently  two 
(rarely  three  or  more)  Protozoa  of  the  same  species 
come  together,  fuse  into  a  single  mass,  and  thus 
become  very  literally  "one  flesh."  This  process  of 
"  conjugation"  is  usually  (though  by  no  means  invari- 
ably) followed  by  a  period  of  quiescent  "encystation"; 
after  which  the  contents  of  the  cyst  escape  in  the  form 
of  a  number  of  minute  particles,  or  "  spores,"  and  these 
severally  develope  into  the  parent  type.  Obviously 
this  process  of  conjugation,  when  it  is  thus  a  pre- 
liminary to  multiplication,  appears  to  be  in  its  essence 
the  same  as  fertilization.  And  if  it  be  objected  that 
encystation  and  spore-formation  in  the  Protozoa  are 
not  always  preceded  by  conjugation  the  answer  would 
be  that  neither  is  oviparous  propagation  in  the  Metazoa 
invariably  preceded  by  fertilization. 

Nevertheless,  that  there  are  great  distinctions 
between  true  sexual  propagation  and  this  fore- 
shadowing of  it  in  conjugation  I  do  not  deny.  The 
question,  however,  is  whether  they  be  so  great  as  to 
justify  any  argument  against  an  historical  continuity 
between  them.  What,  then,  are  these  remaining 
I  2 


n6          Darwin,  and  after  Darwin. 

distinctions?  Briefly,  as  we  have  seen,  they  are  the 
extrusion  from  egg-cells  of  polar  bodies,  and  the 
occurrence,  both  in  egg-cells  and  their  products 
(tissue-cells),  of  the  process  of  karyokinesis.  But,  as 
regards  the  polar  bodies,  it  is  surely  not  difficult  to 
suppose  that,  whatever  their  significance  may  be,  it  is 
probably  in  some  way  or  another  connected  with  the 
high  specialization  of  the  functions  which  an  egg  cell 
has  to  discharge.  Nor  is  there  any  difficulty  in  further 
supposing  that,  whatever  purpose  is  served  by  getting 
rid  of  polar  bodies,  the  process  whereby  they  are  got  rid 
of  was  originally  one  of  utilitarian  development — i.  e. 
a  process  which  at  its  commencement  did  not  betoken 
any  difference  of  kind,  or  breach  of  continuity,  between 
egg-cells  and  cells  of  simpler  constitution. 

Lastly,  with  respect  to  karyokinesis,  although  it 
is  true  that  the  microscope  has  in  comparatively 
recent  years  displayed  this  apparently  important 
distinction  between  unicellular  and  multicellular  or- 
ganisms, two  considerations  have  here  to  be  supplied. 
The  first  is,  that  in  some  of  the  Protozoa  processes 
very  much  resembling  those  of  karyokinesis  have 
already  been  observed  taking  place  in  the  nucleus 
preparatory  to  its  division.  And  although  such  pro- 
cesses do  not  present  quite  the  same  appearances  as 
are  to  be  met  with  in  egg-cells,  neither  do  the  karyo- 
kinetic  processes  in  tissue-cells,  which  in  their  sundry 
kinds  exhibit  great  variations  in  this  respect.  More- 
over, even  if  such  were  not  the  case,  the  bare  fact 
that  nuclear  division  is  not  invariably  of  the  simple 
or  direct  character  in  the  case  of  all  Protozoa,  is 
sufficient  to  show  that  the  distinction  now  before 
us — like  the  one  last  dealt  with — is  by  no  means 


Embryology.  1 1 7 

absolute.  As  in  the  case  of  sexual  propagation,  so 
in  that  of  karyokinesis,  processes  which  are  common 
to  all  the  Metazoa  are  not  wholly  without  their  fore- 
shadowings  in  the  Protozoa.  And  seeing  how  greatly 
exalted  is  the  office  of  egg-cells— and  even  of  tissue- 
cells — as  compared  with  that  of  their  supposed  ancestry 
in  protozoal  cells,  it  seems  to  me  scarcely  to  be 
wondered  at  if  their  specializations  of  function  should 
be  associated  with  corresponding  peculiarities  of 
structure — a  general  fact  which  would  in  no  way 
militate  against  the  doctrine  of  evolution.  Could 
we  know  the  whole  truth,  we  should  probably  find 
that  in  order  to  endow  the  most  primitive  of  egg-cells 
with  its  powers  of  marshalling  its  products  into  a 
living  army  of  cell-battalions,  such  an  egg-cell  must 
have  been  passed  through  a  course  of  developmental 
specialization  of  so  elaborate  a  kind,  that  even  the 
complex  processes  of  karyokinesis  are  but  a  very 
inadequate  expression  thereof. 

Probably  I  have  now  said  enough  to  show  that, 
remarkable  and  altogether  exceptional  as  the  pro- 
perties of  germ-cells  of  the  multicellular  organisms 
unquestionably  show  themselves  to  be,  yet  when  these 
properties  are  traced  back  to  their  simplest  beginnings 
in  the  unicellular  organisms,  they  may  fairly  be  re- 
garded as  fundamentally  identical  with  the  properties 
of  living  cells  in  general.  Thus  viewed,  no  line  of  real 
demarcation  can  be  drawn  between  growth  and  repro- 
duction, even  of  the  sexual  kind.  The  one  process  is, 
so  to  speak  physiologically  continuous  with  the  other ; 
and  hence,  so  far  as  the  pre-embryonic  stage  of  life- 
history  is  concerned,  the  facts  cannot  fairly  be  regarded 
as  out  of  keeping  with  the  theory  of  evolution. 


n8          Darwin,  and  after  Darwin. 

I  will  now  pass  on  to  consider  the  embryogeny  of 
the  Metazoa,  beginning  at  its  earliest  stage  in  the 
fertilization  of  the  ovum.  And  here  it  is  that  the 
constructive  argument  in  favour  of  evolution  which 
is  derived  from  embryology  may  be  said  properly  to 
commence.  For  it  is  surely  in  itself  a  most  suggestive 
fact  that  all  the  Metazoa  begin  their  life  in  the  same 
way,  or  under  the  same  form  and  conditions.  Omne 
vivum  ex  ovo.  This  is  a  formula  which  has  now  been 
found  to  apply  throughout  the  whole  range  of  the 
multicellular  organisms.  And  seeing,  as  we  have  just 
seen,  that  the  ovum  is  everywhere  a  single  cell,  the 
formula  amounts  to  saying  that,  physiologically 
speaking,  every  Metazoon  begins  its  life  as  a  Pro- 
tozoon,  and  every  Metaphyton  as  a  Protophyton ]. 

Now,  if  the  theory  of  evolution  is  true,  what  should 
we  expect  to  happen  when  these  germ-cells  are  fer- 
tilized, and  so  enter  upon  their  severally  distinct 
processes  of  development?  Assuredly  we  should 
expect  to  find  that  the  higher  organisms  pass  through 
the  same  phases  of  development  as  the  lower  or- 
ganisms, up  to  the  time  when  their  higher  characters 
begin  to  become  apparent.  If  in  the  life-history  of 
species  these  higher  characters  were  gained  by  gradual 
improvement  upon  lower  characters,  and  if  the  de- 
velopment of  the  higher  individual  is  now  a  general 
recapitulation  of  that  of  its  ancestral  species,  in  studying 
this  recapitulation  we  should  expect  to  find  the  higher 
organism  successively  unfolding  its  higher  characters 
from  the  lower  ones  through  which  its  ancestral  species 
had  previously  passed.  And  this  is  just  what  we  do 

1  Even  when  propagated  by  budding,  a  mnllicellular  organism  has 
been  ultimately  derived  from  a  germ-cell. 


Embryology.  119 

find.  Take,  for  example,  the  case  of  the  highest 
organism,  Man.  Like  that  of  all  other  organisms, 
unicellular  or  multicellular,  his  development  starts 
from  the  nucleus  of  a  single  cell.  Again,  like  that 
of  all  the  Metazoa  and  Metaphyta,  his  development 
starts  from  the  specially  elaborated  nucleus  of  an 
egg-cell,  or  a  nucleus  which  has  been  formed  by 
the  fusion  of  a  male  with  a  female  element  *.  When 
his  animality  becomes  established,  he  exhibits  the 
fundamental  anatomical  qualities  which  characterize 
such  lowly  animals  as  polyps  and  jelly-fish.  And 
even  when  he  is  marked  off  as  a  Vertebrate,  it  cannot 
be  said  whether  he  is  to  be  a  fish,  a  reptile,  a  bird, 
or  a  beast.  Later  on  it  becomes  evident  that  he  is 
to  be  a  Mammal  ;  but  not  till  later  still  can  it  be  said 
to  which  order-*pf  «mammals  he  belongs. 

Here,  however,  we  must  guard  against  an  error  which 
is  frequently  met  with  in  popular  expositions  of  this 
subject.  It  is  not  true  that  the  embryonic  phases 
in  the  development  of  a  higher  form  always  resemble 
so  many  adult  stages  of  lower  forms.  This  may  or 
may  not  be  the  case  ;  but  what  always  is  the  case 

1  It  has  already  been  stated  that  both  parthenogenesis  and  gemmation 
are  ultimately  derived  fiom  sexual  reproduction.  It  may  now  be  added, 
on  the  other  hand,  that  the  earlier  stages  of  parthenogenesis  have  been 
observed  to  occur  sporadically  in  all  sub-kingdoms  of  the  Metazoa, 
including  the  Vertebrata,  and  even  the  highest  class,  Mammalia.  These 
earlier  stages  consist  in  spontaneous  segmentations  of  the  ovum ;  so 
that  even  if  a  virgin  has  ever  conceived  and  borne  a  son,  and  even  if 
such  a  fact  in  the  human  species  has  been  unique,  still  it  would  not  be- 
token any  breach  of  physiological  continuity.  Indeed,  according  to 
Weismann's  not  improbable  hypothesis  touching  the  physiological 
meaning  of  polar  bodies,  such  a  fact  need  betoken  nothing  more  than 
a  slight  disturbance  of  the  complex  machineiy  of  ovulalion,  on  account 
of  which  the  ovum  failed  to  eliminate  from  its  substance  an  almost 
inconceivably  minute  portion  of  its  nucleus. 


i2O          Darwin,  and  after  Darwin. 

is,  that  the  embryonic  phases  of  the  higher  form 
resemble  the  corresponding  phases  of  the  lower  forms. 
Thus,  for  example,  it  would  be  wrong  to  suppose 
tl.at  at  any  stage  of  his  development  a  man  resembles 
a  jelly-fish.  What  he  does  resemble  at  an  early 
stage  of  his  development  is  the  essential  or  ground- 
plan  of  the  jelly-fish,  which  that  animal  presents  in 
its  embryonic  condition,  or  before  it  begins  to  assume 
its  more  specialized  characters  fitting  it  for  its  own 
particular  sphere  of  life.  The  similarities,  therefore, 
which  it  is  the  function  of  comparative  embryology 
to  reveal  are  the  similarities  of  type  or  morphological 
plan  :  not  similarities  of  specific  detail.  Specific  details 
may  havebeen  added  to  this, that  and  the  other  species 
for  their  own  special  requirements,  after  they  had  seve- 
rally branched  off  from  the  common  ancestral  stem  ; 
and  so  could  not  be  expected  to  recur  in  the  life-history 
of  an  independent  specific  branch.  The  comparison 
therefore  must  be  a  comparison  of  embryo  with 
embryo  ;  not  of  embryos  with  adult  forms. 

In  order  to  give  a  general  idea  of  the  results  thus 
far  yielded  by  a  study  of  comparative  embryology  in 
the  present  connexion,  I  will  devote  the  rest  of  this 
chapter  to  giving  an  outline  sketch  of  the  most  im- 
portant and  best  established  of  these  results. 

Histologically  the  ovum,  or  egg-cell,  is  nearly 
identical  in  all  animals,  whether  vertebrate  or  in- 
vertebrate. Considered  as  a  cell  it  is  of  large  size, 
but  actually  it  is  not  more  than  y^,  and  may  be  less 
than  -5\-$  of  an  inch  in  diameter.  In  man.  as  in  most 
mammals,  it  is  about  T^F.  It  is  a  more  or  less  spherical 
body,  presenting  a  thin  transparent  envelope,  called 


Embryology. 


121 


the  zona  pellucida,  which  contains — first,  the  proto- 
plasmic cell-substance  or  "yolk,"  within  which  lies, 
second,  the  nucleus  or  germinal  vesicle,  within  which 
again  lies,  third,  the  nucleolus  or  germinal  spot.  This 
description  is  true  of  the  egg-cells  of  all  animals, 
if  we  add  that  in  the  case  of  the  lowest  animals — such 
as  sponges,  &c. — there  is  no  enveloping  membrane: 
the  egg-cell  is  here  a  naked  cell,  and  its  constituent 
protoplasm,  being  thus  unconfined,  is  free  to  perform 
protoplasmic  movements,  which  it  does  after  the 


FIG.  30. — Ovarian  orum  of  a  Mammal,  (a)  magnified  and  viewed  under 
pressure,  (£)  burst  by  increased  pressure,  with  yolk  and  nucleus 
escaping  :  (<r)  the  nucleus  more  freed  from  yolk-substance.  (From 
Quaiti's  Anatomy,  after  Allen  Thomson.) 

manner,  and  with  all  the  activity,  of  an  amoeba. 
But  even  with  respect  to  this  matter  of  an  enveloping 
membrane,  there  is  no  essential  difference  between 
an  ovum  of  the  lowest  and  an  ovum  of  the  highest 
animals.  For  in  their  early  stages  of  development 
within  the  ovary  the  ova  of  the  highest  animals 
are  likewise  in  the  condition  of  naked  cells,  exhibiting 
amcebiform  movements ;  the  enveloping  membrane 
of  an  ovum  being  the  product  of  a  later  development. 


FlG  31.— Amoeboid  movements  of  young  egg-cells,  a,  Amitboid  ovum  of  Hydra 
(from  Balfour.  after  Kleinenberg) ;  b,  early  ovum  of  Toxopnenstes  varifgaius^  with 
pseudopodia-like  processes  (from  Balfour,  after  Selenka) ;  c,  ovum  of  Toxopneitsles 
lividus,  more  nearly  ripe  (from  Balfour,  Hertwig).  A  I  to  A  4,  the  primitive  egg-cell 
of  a  Chalk-Sponge  (Leuculmis  echinus),  in  four  successive  conditions  of  motion. 
Bl  to  B8,  ditto  of  a  Hermit-Crab  (Chondracanihus  cornutus),  in  eight  successive 
stages  (after  E.  von  Beneden).  C  I  to  C<>,  ditto  of  a  Cat,  in  five  successive  stages 
(after  Pfluger).  D.  ditto  of  Trout ;  E,  of  a  Hen  ;  F,  of  Man.  The  first  series  is  taken 
from  the  Encycl.  Brit. ;  the  second  from  Hackel's  Evolution  of  Man. 


Embryology.  \  2  ^ 

Moreover  this  membrane,  when  present,  is  usually 
provided  with  one  or  more  minute  apertures,  through 
which  the  spermatozoon  passes  when  fertilizing  the 
ovum.  It  is  remarkable  that  the  spermatozoa  know, 

so  to  speak,  of  the  existence  of  these  gate-ways, 

their  snake-like   movements   being  directed  towards 


FIG.  32. — Human  ovum,  mature  and  greatly  magnified.    (After  Hackel.) 

them,  presumably  by  a  stimulus  due  to  some  emana- 
tion therefrom1.  In  the  mammalian  ovum,  however, 
these  apertures  are  exceedingly  minute,  and  distributed 

'  The  spermatozooids  of  certain  plants  can  be  strongly  attracted 
towards  a  pipette  which  is  filled  with  malic  acid — crowding  around  and 
into  it  with  avidity. 


124  Darwin,  and  after  Darwin. 

all  round  the  circumference  of  the  pellucid  envelope, 
as  represented  in  this  illustration  (Fig.  32). 

In  thus  saying  that  the  ova  of  all  animals  are,  so 
far  as  microscopes  can  reveal,  substantially  similar,  I 
am  of  course  speaking  of  the  egg-cell  proper,  and 
not  of  what  is  popularly  known  as  the  egg.  The  egg 
of  a  bird,  for  example,  is  the  egg-cell,  plus  an  enor- 
mous aggregation  of  nutritive  material,  an  egg-shell, 
and  sundry  other  structures  suited  to  the  subsequent 
development  of  the  egg-cell  when  separated  from  the 
parent's  body.  But  all  these  accessories  are,  from 
our  present  point  of  view,  accidental  or  adventitious. 
What  we  have  now  to  understand  by  the  ovum,  the 
egg,  or  the  egg-cell,  is  the  microscopical  germ  which  I 
have  just  described.  So  far  then  as  this  germ  is 
concerned,  we  find  that  all  multicellular  organisms 
begin  their  existence  in  the  same  kind  of  structure, 
and  that  this  structure  is  anatomically  indistinguishable 
from  that  of  the  permanent  form  presented  by  the 
lowest,  or  unicellular  organisms.  But  although  anato- 
mically indistinguishable,  physiologically  they  present 
the_sundry  peculiarities  already  mentioned. 

N6*w  I  have  endeavoured  to  show  that  none  of 
these^eculiarities  are  such  as  to  exclude — or  even  so 
much  as  to  invalidate  —  the  supposition  of  develop- 
mental continuity  between  the  lowest  egg- cells  and 
the  highest  protozoal  cells.  It  remains  to  show  in  this 
place,  and  on  the  other  hand,  that  there  is  no  breach 
of  continuity  between  the  lowest  and  the  highest  egg- 
cells  ;  but,  on  the  contrary,  that  the  remarkable 
uniformity  of  the  complex  processes  whereby  their 
peculiar  characters  are  exhibited  to  the  histologist,  is 
such  as  of  itself  to  sustain  the  doctrine  of  continuity 


Embryology. 


125 


in  a  singularly  forcible  manner.  On  this  account, 
therefore,  and  also  because  the  facts  will  again  have 
to  be  considered  in  another  connexion  when  we  come 
to  deal  with  Weismann's  theory  of  heredity,  I  will 
here  briefly  describe  the  processes  in  question. 

We  have  already  seen  that  the  young  egg-cell  mul- 
tiplies itself  by  simple  binary  division,  after  the 
manner  of  unicellular  organisms  in  general— thereby 


f.pn.- 


FlG.  33. — Stages  in  the  formation  of  the  polar  bodies  in  the  ovum  of  a 
star-fish.  (After  Hertwig.)  g.v.,  germinal  vesicle  transformed  into  a 
spindle-shaped  system  of  fibres  ;  /.',  the  first  polar  body  becoming  ex- 
truded; p.,  p.,  both  polar  bodies  fully  extruded ',  fpn,,  female  pro- 
nucleus,  or  residue  of  the  germinal  vesicle. 

indicating,  as  also  by  its  amoebiform  movements,  its 
fundamental  identity  with  such  organisms  in  kind. 
But,  as  we  have  likewise  seen,  when  the  ovum  ceases 
to  resemble  these  organisms,  by  taking  on  its  higher 
degree  of  functional  capacity,  it  is  no  longer  able  to 
multiply  itself  in  this  manner.  On  the  contrary,  its 
cell-divisions  are  now  of  an  endogenous  character, 


126          Darwin,  and  after  Darwin. 

and  result  in  the  formation  of  many  different  kinds  of 
cells,  in  the  order  required  for  constructing  the  multi- 
cellular  organism  to  which  the  whole  series  of  processes 
eventually  give  rise.  We  have  now  to  consider  these 
processes  seriatim. 

First  of  all  the  nucleus  discharges  its  polar  bodies, 
as  previously  mentioned,  and  in  the  manner  here 
depicted  on  the  previous  page.  (Fig.  33.)  It  will  be 
observed  that  the  nucleus  of  the  ovum,  or  the  germinal 
2.  3. 


FIG.  34. — Fertilization  of  the  ovum  of  an  echinotlerm.  (From  Quairis 
Anatomy,  after  Selenka.)  S,  spermatozoon  ;  m.pr.,  male  pronucleus; 
f.pr.,  female  pronucleus.  I  to  4  correspond  to  D  to  G  in  the  next 
figure. 

vesicle  as  it  is  called,  gets  rid  first  of  one  and  after- 
wards of  the  other  polar  body  by  an  "  indirect,"  or 
karyokinetic,  process  of  division.  'Fig.  33.)  Extrusion 
of  these  bodies  from  the  ovum  (or  it  may  be  only  from 
the  nucleus)  having  been  accomplished,  what  remains 
of  the  nucleus  retires  from  the  circumference  of  the  ovum, 
and  is  called  the  female  pronucleus.  (Fig.  33.  fpn.) 
The  ovum  is  now  ready  for  fertilization.  A  similar 
emission  of  nuclear  substance  is  said  by  some  good 


Embryology.  i?7 

observers  to  take  place  also  from  the  male  germ-cell, 
or  spermatozoon,  at  or  about  the  close  of  its  develop- 
ment. The  theories  to  which  these  facts  have  given 
rise  will  be  considered  in  future  chapters  on  Heredity. 

Turning  now  to  the  mechanism  of  fertilization,  the 
diagrams  (Figs.  34,  35)  represent  what  happens  in 
the  case  of  star-fish. 

The  sperm-cell  or  spermatozoon,  is  seen  in  the  act 
of  penetrating  the  ovum.  In  the  first  figure  it  has 
already  pierced  the  mucilaginous  coat  of  the  ovum, 


FIG.  35. — Fertilization  of  the  ovum  of  a  star-fish.  (From  the  Encycl. 
Brit,  after  Fol.)  A,  spermatozoa  in  the  mucilaginous  coat  of  the 
ovum  ;  a  prominence  is  rising  from  the  surface  of  the  ovum  towards 
a  spermatozoon  ;  B,  they  have  almost  met ;  C,  they  have  met ;  D, 
the  spermatozoon  enters  the  ovum  through  a  distinct  opening ;  H, 
the  entire  ovum,  showing  extruded  polar  bodies  on  its  upper  surface, 
and  the  moving  together  of  the  male  and  female  pronuclei;  E,  F,  G, 
meeting  and  coalescence  of  the  pronuclei. 

the  limit  of  which  is  represented  by  a  line  through 
which  the  tail  of  the  spermatozoon  is  passing :  the 
head  of  the  spermatozoon  is  just  entering  the  ovum 
proper.  It  may  be  noted  that,  in  the  case  of  many 
animals,  the  general  protoplasm  of  the  ovum  becomes 
aware,  so  to  speak,  of  the  approach  of  a  spermatozoon, 
and  sends  up  a  process  to  meet  it.  (Fig.  35,  A,  B,  C.) 
Several — or  even  many — spermatozoa  may  thus  enter 
the  coat  of  the  ovum  ;  but  normally  only  one  proceeds 
further,  or  right  into  the  substance  of  the  ovum,  for  the 


128  Darwin,  and  after  Darwin. 

purpose  of  effecting  fertilization.  This  spermatozoon, 
as  soon  as  it  enters  the  periphery  of  the  yolk,  or  cell- 
substance  proper,  sets  up  a  series  of  remarkable 
phenomena.  First,  its  own  head  rapidly  increases  in 
size,  and  takes  on  the  appearance  of  a  cell-nucleus  :  this 
is  called  the  male  pronucleus.  At  the  same  time  its 
tail  begins  to  disappear,  and  the  enlarged  head  proceeds 
to  make  its  way  directly  towards  the  nucleus  of  the 
ovum  which,  as  before  stated,  is  now  called  the  female 
pronucleus.  The  latter  in  its  turn  moves  towards  the 
former,  and  when  the  two  meet  they  fuse  into  one 
mass,  forming  a  new  nucleus.  Before  the  two  actually 
meet,  the  spermatozoon  has  lost  its  tail  altogether; 
and  it  is  noteworthy  that  during  its  passage  through 
the  protoplasmic  cell-contents  of  the  ovum,  it  appears 
to  exercise  upon  this  protoplasm  an  attractive  in- 
fluence ;  for  the  granules  of  the  latter  in  its  vicinity 
dispose  themselves  around  it  in  radiating  lines.  All 
these  various  phenomena  are  depicted  in  the  above 
wood-cuts.  (Figs.  34,  35.) 

Fertilization  having  been  thus  effected  by  fusion  of 
the  male  and  female  pronuclei  into  a  single  (or  new) 
nucleus,  this  latter  body  proceeds  to  exhibit  compli- 
cated processes  of  karyokinesis,  which,  as  before 
shown,  are  preliminary  to  nuclear  division  in  the  case 
of  egg-cells.  Indeed  the  karyokinetic  process  may 
begin  in  both  the  pronuclei  before  their  junction  is 
effected;  and,  even  when  their  junction  is  effected, 
it  does  not  appear  that  complete  fusion  of  the  so- 
called  chromatin  elements  of  the  two  pronuclei  takes 
place.  For  the  purpose  of  explaining  what  this 
means,  and  still  more  for  the  purpose  of  giving  a 
general  idea  of  the  karyokinetic  processes  as  a  whole, 


Embryology.  129 

I  will  quote  the  following  description  of  them,  because, 
for  terseness  combined  with  lucidity,  it  is  unsur- 
passable. 

Researches,  chiefly  due  to  Flemming,  have  shown  that  the 
nucleus  in  very  many  tissues  of  higher  plants  and  animals  con- 
sists of  a  capsule  containing  a  plasma  of  "  achromatin,"  not  deeply 


FIG.  36. — Karyokinesis  of  a  typical  tissue-cell  (epithelium  of  Sala- 
mander). (After  Flemming  and  Klein.)  The  series  from  A  to  I 
represents  the  successive  stages  in  the  movement  of  the  chromatin 
fibres  during  division,  excepting  G,  which  represents  the  "  nucleus- 
spindle  "  of  an  egg-cell.  A,  resting  nucleus ;  D,  wreath-form ;  E, 
single  star,  the  loops  of  the  wreath  being  broken  ;  F,  separation  of 
the  star  into  two  groups  of  U-shaped  fibres ;  H,  diaster  or  double 
star;  I,  completion  of  the  cell-division  and  formation  of  two  resting 
nuclei.  In  G  the  chromatin  fibres  are  marked  a,  and  correspond  to 
the  "equatorial  plate";  b,  achromatin  fibres  forming  the  nucleus- 
spindle;  c,  granules  of  the  cell-protoplasm  forming  a  "polar  star." 
Such  a  polar  star  is  seen  at  each  end  of  the  nucleus-spindle,  and  is 
not  to  be  confused  with  the  diaster  H,  the  two  ends  of  which  are 
composed  of  chromatin. 

stained  by  re-agents,  ramifying  in  which  is  a  reticulum  of  "  chro- 
matin "  consisting  of  fibres  which  readily  take  a  deep  stain. 
(Fig.  36,  A).  Further  it  is  demonstrated  that,  when  the  cell  is 
about  to  divide  into  two,  definite  and  very  remarkable  move- 
ments take  place  in  the  nucleus,  resulting  in  the  disappearance 
of  the  capsule  and  in  the  arrangement  of  its  fibres  first  in  the 
*  K 


130          Darwin,  and  after  Darwin. 

form  of  a  wreath  (D),  and  subsequently  (by  the  breaking  of 
the  loops  formed  by  the  fibres)  in  the  form  of  a  star  (E).  A 
further  movement  within  the  nucleus  leads  to  an  arrangement  of 
the  broken  loops  in  two  groups  (F),  the  position  of  the  open  ends 
of  the  broken  loops  being  reversed  as  compared  with  what  pre- 
viously obtained.  Now  the  two  groups  diverge,  and  in  many 
cases  a  striated  appearance  of  the  achromatin  substance  between 
the  two  groups  of  chromatin  loops  is  observable  (H).  In  some 
cases  (especially  egg-cells)  this  striated  arrangement  of  the 
achromatin  is  then  termed  a  "  nucleus-spindle,"  and  the  group  of 
chromatin  loops  (G,  a)  is  known  as  "  the  equatorial  plate."  At  each 
end  of  the  nucleus-spindle  in  these  cases  there  is  often  seen  a 
star  consisting  of  granules  belonging  to  the  general  protoplasm 
of  the  cell  (G,  c].  These  are  known  as  "  polar  stars."  After  the 
separation  of  the  two  sets  of  loops  (H)  the  protoplasm  of  the 
general  substance  of  the  cell  becomes  constricted,  and  division 
occurs,  so  as  to  include  a  group  of  chromatin  loops  in  each  of  the 
two  fission  products.  Each  of  these  then  rearranges  itself  to- 
gether with  the  associated  chromatin  into  a  nucleus  such  as  was 
present  in  the  mother  cell  to  commence  with  (I)1. 

Since  the  above  was  published,  however,  further 
progress  has  been  made.  In  particular  it  has  been 
found  that  the  chromatin  fibres  pass  from  phase  D 
to  phase  F  by  a  process  of  longitudinal  splitting  (Fig. 
37  g,  h  ;  Fig.  38,  VI,  VII)— which  is  a  point  of  great 
importance  for  Weismann's  theory  of  heredity, — and 
that  the  protoplasm  outside  the  nucleus  seems  to 
take  as  important  a  part  in  the  karyokinetic  process 
as  does  the  nuclear  substance.  For  the  so-called 
"attraction-spheres"  (Fig.  38  II  a,  III,  III  a,  VIII  to 
XII),  which  were  at  first  supposed  to  be  of  subordinate 
importance  in  the  process  as  a  whole,  are  now  known 
to  take  an  exceedingly  active  part  in  it  (see  especially 
IX  to  XI).  Lastly,  it  may  be  added  that  there  is  a 

1  Ray  Lankester,  Encydop.  Brit.,  9th  ed.,  Vol.  XIX,  pp.  832-3. 


Embryology. 


,  fi 

/,  the  final  result  of  this  fdiafterV  'Pfratl0"  °f  the  filaments  »to  two  groups  ; 
cell  into  two,  showing  increasTnTconL  *  §i|  -T  V,"  the  dlvisi°n  °f  the  ^ 
resting  stage  at  y  .  >rtlOD  °f  the  fi^tnent8,  until  they  reach  the 


K  2 


132  Darwin,  and  after  Darwin. 

11  a. 


FlG.  38.—  Formation  and  conjugation  of  the  pronuclei  in  Ascaris  megalocephala. 
(From  Quoin's  Anatomy,  after  E.  von  Beneden.)  f^  female  pronucleus  ;  m, 
male  pronucleus  ;  J>,  one  of  the  polar  bodies. 

I.  The  second  polar  lx>dy  has  just  lieen  extruded  ;  both  male  and  female  pronuclei 
contain  two  chromatin  particles  ;   those  of  the  male  pronucleus  are  becoming 
transformed  into  a  skein. 

II.  The  chromatin  in  both  pronuclei  now  forms  into  a  skein. 

II  a.  The  skeins  are  more  distinct.  Two  attraction  (or  protoplasmic)  spheres,  each 
with  a  central  particle  united  with  a  small  spindle  of  achromatic  fibres,  have  made 
their  appearance  in  the  general  substance  of  the  egg  close  to  the  mutually 
approaching  pronuclei.  The  male  pronucleus  has  the  remains  of  the  body  of  the 
spermatozoon  adhering  to  it. 

III.  On'v  the  female  pronucleus  is  shown  in  this  figure.    The  skein  is  contracted 

ened.     The  attraction-spheres 


ide  of  the  ovum,  and  are 
of  fibres  forming  a  polar  circle,  f.c.  ;  e.c., 


nd  thicke 

connected  with  its  periphery  by  a 
equatorial  circle. 

Ill  a.    The  pronuclei  have  come  into  contact,  and  the  spindle-system  is  now 
arranged  across  their  common  axis. 

IV.  Contraction  of  the  skein,  and  formation  of  two  U-  or  V-shaped  chromatin 
fibres  in  each  pronucleus. 

V.  The  V-shaped  chromatin  filaments  are  now  quite  distinct  :  the  male  and  female 
pronuclei  are  in  close  contact. 


Embryology. 


133 


XI. 


XII. 


VI.,  VII.  The  V-shaped  filaments  are  splitting  longitudinally  ;  their  structure  of  fine 
granules  of  chromatin  is  apparent  in  VII.,  which  is  more  highly  magnified.  The 
conjugation  of  the  pronuclei  is  apparently  complete  in  Vll.  The  attraction- 
spheres  and  achromatic  spindle,  although  present,  are  not  depicted  in  IV.,  V., 
VI,  and  VII. 

VIII.  Equatorial  arrangement  of  the  four  chromatin  loops  in  the  middle  of  the 
now  segmenting  ovum  :   the  achromatic  substance  forming   a  spindle-shaped 
system  of  granules  with  fibres  radiating  from  the  poles  of  the  spindle  (attraction- 
spheres);  the  chromatin  forms  an  equatorial  plate.     (Compare  Fig.  36  G.) 

IX.  Shows  diagrammatically  the  commencing  separation  of  the  chromatin  fibres 
of  the  conjugated  nuclei,  and  the  system  ot  fibres  radiating  from  the  attraction- 
spheres.    (Compare  again  Fig.  36  G.)     f.c.t  polar  circle ;  e.c.,  equatorial  circle  ; 
e.g.,  central  particle. 

X.  Further  separation  of  the  chromatin  filamentm.     Each  of  the  central  particles 
of  the  attraction-spheres  has  divided  into  two. 

XI.  The  chromatin  fibres  are  becoming  developed  into  the  skeins  of  the  two 
daughter-nuclei.    These  are  still  united  by  fibres  of  achromatin.    The  general 
protoplasm  of  the  ovum  is  becoming  divided. 

XII.  The  two  daughter-nuclei  exhibit  a  chromatin  network.   Each  of  the  attraction- 
spheres  has  divided  into  two,  which  are  joined  by  fibres  of  achromatin,  and  con- 
nected with  the  periphery  of  the  cell  in  the  same  way  as  in  the  original  or  parent 
sphere,  III. 


134          Darwin,  and  after  Darwin. 

growing  consensus  of  authoritative  opinion,  that  the 
chromatin  fibres  are  the  seats  of  the  material  of 
heredity,  or,  in  other  words,  that  they  contain  those 
essential  elements  of  the  cell  which  endow  the 
daughter-cells  with  their  distinctive  characters.  There- 
fore, where  the  parent-cell  is  an  ovum,  it  follows  from 
this  view  that  all  hereditary  qualities  of  the  future 
organism  are  potentially  present  in  the  ultra-micro- 
scopical structure  of  the  chromatin  fibres. 

As  I  shall  have  more  to  say  about  these  processes 
in  the  next  volume,  when  we  shall  see  the  important 
part  which  they  bear  in  Weismann's  theory  of 
heredity,  it  is  with  a  double  purpose  that  I  here 
introduce  these  yet  further  illustrations  of  them  upon  a 
somewhat  larger  scale.  The  present  purpose  is  merely 
that  of  showing,  more  clearly  than  hitherto,  the  great 
complexity  of  these  processes  on  the  one  hand,  and, 
on  the  other,  the  general  similarity  which  they  display 
in  egg-cells  and  in  tissue-cells.  But  as  in  relation  to 
this  purpose  the  illustrations  speak  for  themselves,  I 
may  now  pass  on  at  once  to  the  history  of  embryonic 
development,  which  follows  fertilization  of  the  ovum. 

We  have  seen  that  when  the  new  nucleus  of  the 
fertilized  ovum  (which  is  formed  by  a  coalescence  of  the 
male  pronucleus  with  the  female)  has  completed  its 
karyokinetic  processes,  it  is  divided  into  two  equal 
parts  ;  that  these  are  disposed  at  opposite  poles  of  the 
ovum  ;  and  that  the  whole  contents  of  the  ovum  are 
thereupon  likewise  divided  into  two  equal  parts,  with 
the  result  that  there  are  now  two  nucleated  cells  within 
the  spherical  wall  of  the  ovum  where  before  there  had 
only  been  one.  Moreover,  we  have  also  seen  that  a 


Embryology. 


135 


precisely  similar  series  of  events  repeat  themselves  in 
each  of  these  two  cells,  thus  giving  rise  to  four  cells 


FIG.  39. — Segmentation  of  ovum.  (After  Hack  el.)  Successive  stages 
are  marked  by  the  letters  A,  B,  C.  D  represents  several  stages  in 
advance  of  C. 

(see  Fig.  29).  It  must  now  be  added  that  such 
duplication  is  continued  time  after  time,  as  shown  in 
the  accompanying  illustrations  (Figs.  39,  40). 

All  this,  it  will  be  noticed,  is 
a  case  of  cell- multiplication, 
which  differs  from  that  which 
takes  place  in  the  unicellular 
organisms  only  in  its  being  in- 
variably preceded  (as  far  as  we 
know)  by  karyokinesis,  and  in 
the  resulting  cells  being  all  con- 
fined within  a  common  envelope, 
and  so  in  not  being  free  to 
separate.  Nevertheless,  from 
what  has  already  been  said,  it 
will  also  be  noticed  that  this  feature  makes  all  the 
difference  between  a  Metazoon  and  a  Protozoon  ;  so 
that  already  the  ovum  presents  the  distinguishing 
character  of  a  Metazoon. 


FIG.  40. — The  contents  of 
an  ovum  in  an  advanced 
stage  of  segmentation, 
drawn  in  perspective. 
(After  Hackel.) 


136          Darwin,  and  after  Darwin. 

I  have  dealt  thus  at  considerable  length  upon  the 
processes  whereby  the  originally  unicellular  ovum  and 
spermatozoon  become  converted  into  the  multicellular 
germ,  because  I  do  not  know  of  any  other  exposition 
of  the  argument  from  Embryology  where  this,  the  first 
stage  of  the  argument,  has  been  adequately  treated. 
Yet  it  is  evident  that  the  fact  of  all  the  processes 
above  described  being  so  similar  in  the  case  of  sexual 
(or  metazoal)  reproduction  among  the  innumerable  or- 
ganisms where  it  occurs,  constitutes  in  itself  a  strong 
argument  in  favour  of  evolution.  For  the  mechanism 
of  fertilization,  and  all  the  processes  which  even  thus 
far  we  have  seen  to  follow  therefrom,  are  hereby 
shown  to  be  not  only  highly  complex,  but  likewise 
highly  specialized.  Therefore,  the  remarkable  simi- 
larity which  they  present  throughout  the  whole  animal 
kingdom — not  to  speak  of  the  vegetable — is  expressive 
of  organic  continuity,  rather  than  of  absolute  dis- 
continuity in  every  case,  as  the  theory  of  special 
creation  must  necessarily  suppose.  And  it  is  evident 
that  this  argument  is  strong  in  proportion  to  the 
uniformity,  the  specialization,  and  the  complexity  of 
the  processes  in  question. 

Having  occupied  so  much  space  with  supplying  what 
appear  to  me  the  deficiencies  in  previous  expositions 
of  the  argument  from  Embryology,  I  can  now  afford 
to  take  only  a  very  general  view  of  the  more  important 
features  of  this  argument  as  they  are  successively  fur- 
nished by  all  the  later  stages  of  individual  development. 
But  this  is  of  little  consequence,  seeing  that  from  the 
point  at  which  we  have  now  arrived  previous  exposi- 
tions of  the  argument  are  both  good  and  numerous. 
The  following  then  is  to  be  regarded  as  a  mere  sketch 


Embryology.  137 

of  the  evidences  of  phyletic  (or  ancestral)  evolution, 
which  are  so  abundantly  furnished  by  all  the  subse- 
quent phases  of  ontogenetic  (or  individual)  evolution. 
The  multicellular  body  which  is  formed  by  the 
series  of  segmentations  above  described  is  at  first  a 
sphere  of  cells  (Fig.  40).  Soon,  however,  a  watery 
fluid  gathers  in  the  centre,  and  progressively  pushes 
the  cells  towards  the  circumference,  until  they  there 


FIG.  41. — Formation  of  the  gastrula  of  Amphioxus.  (After  Kowalevsky. ) 
A,  wall  of  the  ovum,  composed  of  a  single  layer  of  cells  ;  B,  a  stage 
in  the  process  of  gastrulation ;  C,  completion  of  the  process;  S, 
original  or  segmentation  cavity  »f  ovum ;  al,  alimentary  cavity  of 
gastrula ;  ect,  outer  layer  of  cells ;  ent,  inner  layer  of  cells ;  b,  orifice, 
constituting  the  mouth  in  permanent  forms. 

constitute  a  single  layer.  The  ovum,  therefore,  is  now 
in  the  form  of  a  hollow  sphere  containing  fluid,  con- 
fined within  a  continuous  wall  of  cells  (Fig.  41  A).  The 
next  thing  that  happens  is  a  pitting  in  of  one  portion  of 
the  sphere  (B).  The  pit  becomes  deeper  and  deeper, 
until  there  is  a  complete  imagination  of  this  part  of  the 
sphere — the  cellswhich  constitute  it  being  progressively 


138  Darwin,  and  after  Darwin. 

pushed  inwards  until  they  come  into  contact  with 
those  at  the  opposite  pole  of  the  ovum.  Consequently, 
instead  of  a  hollow  sphere  of  cells,  the  ovum  now 
becomes  an  open  sac,  the  walls  of  which  are  composed 


FIG.  42. — Gastrulation.  A,  Gastrula  of  a  Zoophyte  (Gastrophysema). 
(After  Hackel.)  B,  Gastrula  of  a  Worm  (Sagitta).  (After  Kownlevsky.) 
C,  Gastrula  of  an  Echinoderm  (Uraster).  (After  A.  Agassiz.)  D, 
Gastrula  of  an  Arthropod  (Nauplius}.  (After  Hackel.)  E,  Gastrula 
of  a  Mollusk  (Limnaus).  (After  Rabl.)  F,  Gastrula  of  a  Vertebrate 
(Amphioxus).  (After  Kowalevsky.)  In  all,  d,  indicates  the  intestinal 
cavity ;  o.  the  primitive  mouth ;  s,  the  cleavage-cavity ;  i,  the  endo- 
derm,  or  intestinal  layer ;  e,  the  ectoderm  or  skin-layer. 

of  a  double  layer  of  cells  (C).  The  ovum  is  now  what 
has  been  called  a  gastrula ;  and  it  is  of  importance  to 
observe  that  probably  all  the  Metazoa  pass  through 


Embryology. 


139 


this  stage.  At  any  rate  it  has  been  found  to  occur  in  all 
the  main  divisions  of  the  animal  kingdom,  as  a  glance  at 
the  accompanying  figures  will  serve  to  show  (Fig.  42)  l. 
Moreover  many  of  the  lower  kinds  of  Metazoa  never 
pass  beyond  it ;  but  are  all  their  lives  nothing  else  than 


FIG.  43. — Gastrula  of  a  Chnlk  Sponge.  (After  Hackel.)  A,  External 
view.  B,  Longitudinal  section,  g,  digestive  cavities;  o,  mouth ; 
*,  endoderm  ;  e,  ectoderm. 

gastrulae,  wherein  the  orifice  becomes  the  mouth  of 
the  animal,  the  internal  or  invaginated  layer  of  cells 
the  stomach,  and  the  outer  layer  the  skin.  So  that 
if  we  take  a  child  s  india-rubber  ball,  of  the  hollow 

1  In  most  vertebrated  animals  this  process  of  gastrulation  has  been 
more  or  less  superseded  by  another,  which  is  called  delamination ;  but 
it  scarcely  seems  necessary  for  our  present  purposes  to  describe  the 
latter.  For  not  only  does  it  eventually  lead  to  the  same  result  as 
gastrulation — i.e.  the  converting  of  the  ovum  into  a  double-walled  sac, — 
but  there  is  good  evidence  among  the  lower  Verlebrata  of  its  being  pre- 
ceded by  gastrulation ;  so  that,  even  as  to  the  higher  Vertebrata, 
embryolof,>ists  are  pretty  well  agreed  that  delamination  has  been  but  a 
later  development  of,  or  possibly  improvement  upon,  gastrulation. 


140          Darwin,  and  after  Darwin. 

kind  with  a  hole  in  it,  and  push  in  one  side  with  our 
fingers  till  internal  contact  is  established  all  round,  by 
then  holding  the  indented  side  downwards  we  should 
get  a  very  fair  anatomical  model  of  a  gastraea  form, 


FlG.  44. — Prophysema  primordiale,  an  extant  gastroM-form.  (After 
Hackel.)  (A).  External  view  of  the  whole  animal,  attached  by  its  foot 
to  seaweed.  (B).  Longitudinal  section  of  the  same.  The  digestive 
cavity  (d)  opens  at  its  upper  end  in  the  month  (/«).  Among  the  cells 
of  the  endoderm  {g)  lie  amoeboid  egg-cells  of  large  size  (e).  The  ec- 
toderm (A)  is  encrusted  with  grains  of  sand,  above  the  sponge  spicules. 

such  as  is  presented  by  the  adult  condition  of  many 
of  the  most  primitive  Metazoa — especially  the  lower 
Ccelenterata.  The  preceding  figures  represent  two 


Embryology.  141 

other  such  forms  in  nature,  the  first  locomotive  and 
transitory,  the  second  fixed  and  permanent  (Figs. 
43,  44). 

Here,  then,  we  leave  the  lower  forms  of  Metazoa  in 
their  condition  of  permanent  gastrulae.  They  differ 
from  the  transitory  stage  of  other  Metazoa  only  in 
being  enormously  larger  (owing  to  greatly  further 
growth,  without  any  further  development  as  to  matters 
of  fundamental  importance),  and  in  having  sundry 
tentacles  and  other  organs  added  later  on  to  meet 
their  special  requirements.  The  point  to  remember 
is,  that  in  all  cases  a  gastrula  is  an  open  sac  composed 
of  two  layers  of  cells — the  outer  layer  being  called  the 
ectoderm,  and  the  inner  the  endoderm.  They  have 
also  been  called  the  animal  layer  and  the  vegetative 
layer,  because  it  is  the  outer  layer  (ectoderm)  that 
gives  rise  to  all  the  organs  of  sensation  and  move- 
ment— viz.  the  skin,  the  nervous  system,  and  the 
muscular  system  ;  while  it  is  the  inner  layer  (endoderm) 
that  gives  rise  to  all  the  organs  of  nutrition  and 
reproduction.  It  is  desirable  only  further  to  explain 
that  gastrulation  does  not  take  place  in  all  the  Metazoa 
after  exactly  the  same  plan.  In  different  lines  of 
descent  various  and  often  considerable  modifications 
of  the  original  and  most  simple  plan  have  been  intro- 
duced ;  but  I  will  not  burden  the  present  exposition 
by  describing  these  modifications l.  It  is  enough  for  us 
that  they  always  end  in  the  formation  of  the  two 
primary  layers  of  ectoderm  and  endoderm. 

The  next  stage  of  differentiation  is  common  to  all 
the  Metazoa,  except  those  lowest  forms  which,  as  we 

1  The  most  extreme  of  them  is  that  which  is  mentioned  in  the  last 
foot-note. 


142          Darwin,  and  after  Darwin. 

have  just  seen,  remain  permanently  as  large  gastrulae, 
with  sundry  specialized  additions  in  the  way  of 
tentacles,  £c.  This  stage  of  differentiation  consists  in 
the  formation  of  either  a  pouch  or  an  additional 
layer  between  the  ectoderm  and  the  endoderm,  which 
is  called  the  mesoderm.  It  is  probably  in  most  cases 
derived  from  the  endoderm,  but  the  exact  mode  of  its 
derivation  is  still  somewhat  obscure.  Sometimes  it 
has  the  appearance  of  itself  constituting  two  layers  ; 
but  it  is  needless  to  go  into  these  details  ;  for  in  any 
case  the  ultimate  result  is  the  same — viz.  that  of  con- 
verting the  Metazoon  into  the  form  of  a  tube,  the  walls 
of  which  are  composed  of  concentric  layers  of  cells. 
The  outermost  layer  afterwards  gives  rise  to  the 
epidermis  with  its  various  appendages,  and  also  to  the 
central  nervous  system  with  its  organs  of  special  sense. 
The  median  layer  gives  rise  to  the  voluntary  muscles, 
bones,  cartilages,  &c.,  the  nutritive  systems  of  the 
blood,  the  chyle,  the  lymph,  and  the  muscular  tube 
of  the  intestine.  Lastly,  the  innermost  layer  deve- 
lopes  into  the  epithelium  lining  of  the  intestine, 
with  its  various  appendages  of  liver,  lungs,  intestinal 
glands,  &c. 

I  have  just  said  that  this  three  or  four  layered  stage 
is  shared  by  all  the  Metazoa,  except  those  very  lowest 
forms — such  as  sponges  and  jelly-fish — which  do  not 
pass  on  to  it.  But  from  this  point  the  developmental 
histories  of  all  the  main  branches  of  the  Metazoa 
diverge — the  Vermes,  the  Echinodermata,  the  Mol- 
lusca,  the  Articulata,  and  the  Vertebrata,  each  taking 
a  different  road  in  their  subsequent  evolution.  I  will 
therefore  confine  attention  to  only  one  of  these 
several  roads  or  methods,  namely,  that  which  is 


Embryology.  143 

followed  by  the  Vertebrata— observing  merely  that,  if 
space  permitted,  the  same  principles  of  progressive 
though  diverging  histories  of  evolution  would  equally 
well  admit  of  being  traced  in  all  the  other  sub-king- 
doms which  have  just  been  named. 

In  order  to  trace  these  principles  in  the  case  of  the 
Vertebrata,  it  is  desirable  first  of  all  to  obtain  an  idea 
of  the  anatomical  features  which  most  essentially  dis- 
tinguish the  sub-kingdom  as  a  whole.  The  following, 


FIG.  45. — Ideal  primitive  vertebiate,  seen  from  the  left  side.  (After 
Hackel.)  na,  nose;  au,  eye;  g,  ear;  md,  mouth  ;  ks,  gill-openings; 
x,  notochord;  mr,  spinal  tube  ;  kg,  gill-vessels;  k,  gill-intestine;  hz, 
heart ;  ms,  muscles ;  ma,  stomach  ;  v,  intestinal  vein  ;  c,  body-cavity  ; 
a,  aorta  ;  /,  liver ;  d,  small  intestine  ;  e,  ovary ;  h,  testes ;  n,  kidney 
canal ;  of,  anus ;  Ih,  true  or  leather-skin ;  oh,  outer-skin  (epidermis) ; 
/,  skin-fold,  acting  as  a  fin. 

then,  is  what  may  be  termed  the  ideal  plan  of  verte- 
brate organization,  as  given  by  Prof.  Hackel.  First, 
occupying  the  major  axis  of  body  we  perceive  the 
primitive  vertebral  column.  The  parts  lying  above 
this  axis  are  those  which  have  been  developed  from 
the  ectoderm  and  mesoderm — viz.  voluntary  muscles, 
central  nervous  system,  and  organs  of  special  sense. 
The  parts  lying  below  this  axis  are  for  the  most  part 
those  which  have  been  developed  from  the  endoderm 


144          Darwin,  and  after  Darwin. 

— namely,  the  digestive  tract  with  its  glandular  ap- 
pendages, the  circulating  system  and  the  respiratory 
system.  In  transverse  section, 
therefore,  the  ideal  vertebrate 
consists  of  a  solid  axis,  with  a 
small  tube  occupied  by  the 
nervous  system  above,  and  a 
large  tube,  or  body -cavity, 
below.  This  body-cavity  con- 
tains the  viscera,  breathing 

FIG.    40.  —  The   same  .       .  .  . 

in  transverse  section       organs,    and     heart,     with    its 

through  the  ovaries;       prolongations     into    the     main 

££X  V  "*       blood-vessels  of   the_  organism. 

Lastly,   on    either  side   of  the 

central  axis  are  to  be  found  large  masses  of  muscle — 

two  on  the  dorsal  and  two  on  the  ventral.     As  yet, 

however,  there   are    no   limbs,   nor   even    any   bony 

skeleton,  for  the  primitive  vertebral  column  is  hitherto 

unossified  cartilage.    This  ideal  animal,  therefore,  is  to 

all  appearance  as  much  like  a  worm  as  a  fish,  and  swims 

by  means  of  a  lateral  undulation  of  its  whole  body, 

assisted,  perhaps,  by  a  dorsal  fin  formed  out  of  skin. 

Now  I  should  not  have  presented  this  ideal  repre- 
sentation of  a  primitive  vertebrate — for  I  have  very 
little  faith  in  the  "  scientific  use  of  the  imagination  " 
where  it  aspires  to  discharge  the  functions  of  a  Creator 
in  the  manufacture  of  archetypal  forms — I  say  I  should 
not  have  presented  this  ideal  representative  of  a 
primitive  vertebrate,  were  it  not  that  the  ideal  is 
actually  realized  in  a  still  existing  animal.  For  there 
still  survives  what  must  be  an  immensely  archaic 
form  of  vertebrate,  whose  anatomy  is  almost  identical 
with  that  of  the  imaginary  type  which  has  just  been 


146          Darwin,  and  after  Darwin. 

described.  I  allude,  of  course,  to  Amphioxus,  which 
is  by  far  the  most  primitive  or  generalized  type  of 
vertebrated  animal  hitherto  discovered.  Indeed,  we 
may  say  that  this  remarkable  creature  is  almost  as 
nearly  allied  to  a  worm  as  it  is  to  a  fish.  For  it  has 
no  specialized  head,  and  therefore  no  skull,  brain, 
or  jaws  :  it  is  destitute  alike  of  limbs,  of  a  centralized 
heart,  of  developed  liver,  kidneys,  and,  in  short,  of 
most  of  the  organs  which  belong  to  the  other 
Vertebrata.  It  presents,  however,  a  rudimentary  back- 
bone, in  the  form  of  what  is  called  a  notochord.  Now 
a  primitive  dorsal  axis  of  this  kind  occurs  at  a  very 
early  period  of  embryonic  life  in  all  vertebrated 
animals ;  but,  with  the  exception  of  Amphioxns,  in 
all  other  existing  Vertebrata  this  structure  is  not 
itself  destined  to  become  the  permanent  or  bony 
vertebral  column.  On  the  contrary,  it  gives  way  to, 
or  is  replaced  by,  this  permanent  bony  structure  at 
a  later  stage  of  development.  Consequently,  it  is  very 
suggestive  that  so  distinctively  embryonic  a  structure 
as  this  temporary  cartilaginous  axis  of  all  the  other 
known  Vertebrata  should  be  found  actually  persisting 
to  the  present  day  as  the  permanent  axis  of  Amphioxus. 
In  many  other  respects,  likewise,  the  early  embryonic 
history  of  other  Vertebrata  refers  us  to  the  permanent 
condition  of  Amphioxus.  In  particular,  we  must 
notice  that  the  wall  of  the  neck  is  always  perforated 
by  what  in  Amphioxus  are  the  gill-openings,  and  that 
the  blood-vessels  as  they  proceed  from  the  heart  are 
always  distributed  in  the  form  of  what  are  called 
gill-arches,  adapted  to  convey  the  blood  round  or 
through  the  gills  for  the  purpose  of  aeration.  In  all 
existing  fish  and  other  gill -breathing  Vertebrata  this 


Embryology.  1 4  7 

arrangement  is  permanent.  It  is  likewise  met  with  in  a 
peculiar  kind  of  worm,  called  Balanoglossus — a  creature 
so  peculiar,  indeed,  that  it  has  been  constituted  by 
Gegenbaur  a  class  all  by  itself.  We  can  see  by  the 
wood-cuts  that  it  presents  a  series  of  gill-slits,  like  the 
homologous  parts  of  the  fishes  with  which  it  is  compared 
— i.e.  fishes  of  a  comparatively  low  type  of  organization, 
which  dates  from  a  time  before  the  development  of 
external  gills.  (Figs.  48,  49,  50.)  Now,  as  I  have 
already  said,  these  g\\\-slits  are  supported  internally  by 
the  gi\\-arches,  or  the  blood-vessels  which  convey  the 
blood  to  be  oxygenized  in  the  branchial  apparatus 
(see  below,  Figs.  51,  52,  53) ;  and  the  whole  arrange- 
ment is  developed  from  the  anterior  part  of  the  in- 
testine— as  is  likewise  the  respiratory  mechanism 
of  all  the  gill-breathing  Vertebrata.  That  so  close 
a  parallel  to  this  peculiar  mechanism  should  be  met 
with  in  a  worm,  is  a  strong  additional  piece  of  evidence 
pointing  to  the  derivation  of  the  Vertebrata  from  the 
Vermes. 

Well,  I  have  just  said  that  in  all  the  gill-breathing 
Vertebrata,  this  mechanism  of  gill-slits  and  vascular 
gill-arches  in  the  front  part  of  the  intestinal  tract  is 
permanent.  But  in  the  air-breathing  Vertebrata  such 
an  arrangement  would  obviously  be  of  no  use.  Con- 
sequently, the  gill-slits  in  the  sides  of  the  neck  (see 
Figs.  16  and  57,  58),  and  the  gill-arches  of  the  large 
blood-vessels  (Figs.  54,  55,  56),  are  here  exhibited 
only  as  transitory  phases  of  development.  But  as 
such  they  occur  in  all  air-breathing  Vertebrata.  And, 
as  if  to  make  the  homologies  as  striking  as  possible, 
at  the  time  when  the  gill-slits  and  the  gill -arches  are 
developed  in  the  embryonic  young  of  air-breathing 
L  a 


a  a 

8  « 


FIG.  57. — A  series  of  embryos  at  three  comparable  and  progressive  stages  of 
development  (marked  I,  II,  III),  representing  each  of  the  classes  of  vertebrated 
animals  below  the  Mammalia.  (After  Hackel.) 


FIG.  58.— Another  series  of  embryos,  also  at  three  comparable  and  progressive 
stages  of  development  (marked  I,  II,  HI),  representing  four  different  divisions 
of  the  class  Mammalia.  (After  Hackel.) 


154          Darwin,  and  after  Darwin. 

Vertebrata,  the  heart  is  constructed  upon  the  fish-like 
type.  That  is  to  say,  it  is  placed  far  forwards,  and, 
from  having  been  a  simple  tube  as  in  Worms,  is  now 
divided  into  two  chambers,  as  in  Fish.  Later  on  it 
becomes  progressively  pushed  further  back  between 
the  developing  lungs,  while  it  progressively  acquires 
the  three  cavities  distinctive  of  Amphibia,  and  finally 
the  four  cavities  belonging  only  to  the  complete 
double  circulation  of  Birds  and  Mammals.  Moreover, 
it  has  now  been  satisfactorily  shown  that  the  lungs 
of  air-breathing  Vertebrata,  which  are  thus  destined 
to  supersede  the  function  of  gills  are  themselves  the 
modified  swim-bladder  or  float,  which  belongs  to  Fish. 
Consequently,  all  these  progressive  modifications  in 
the  important  organs  of  circulation  and  respiration  in 
the  air-breathing  Vertebrata,  together  'make  up  as 
complete  a  history  of  their  aquatic  pedigree  as  it 
would  be  possible  for  the  most  exacting  critic  to 
require. 

If  space  permitted,  it  would  be  easy  to  present 
abundance  of  additional  evidence  to  the  same  effect 
from  the  development  of  the  skeleton,  the  skull,  the 
brain,  the  sense-organs,  and,  in  short,  of  every  con- 
stituent part  of  the  vertebrate  organization.  Even 
without  any  anatomical  dissection,  the  similarity  of 
all  vertebrated  embryos  at  comparable  stages  of  de- 
velopment admits  of  being  strikingly  shown,  if  we 
merely  place  the  embryos  one  beside  the  other. 
Here,  for  instance,  are  the  embryos  of  a  fish,  a  sala- 
mander, a  tortoise,  a  bird,  and  four  different  mammals. 
In  each  case  three  comparable  stages  of  development 
are  represented.  Now,  if  we  read  the  series  horizontally, 
we  can  see  that  there  is  very  little  difference  between 


Embryology.  155 

the  eight  animals  at  the  earliest  of  the  three  stages 
represented — all  having  fish-like  tails,  gill-slits,  and 
so  on.  In  the  next  stage  further  differentiation  has 
taken  place,  but  it  will  be  observed  that  the  limbs 
are  still  so  rudimentary  that  even  in  the  case  of  Man 
they  are  considerably  shorter  than  the  tail.  But  in 
the  third  stage  the  distinctive  characters  are  well 
marked. 

So  much  then  for  an  outline  sketch  of  the  main 
features  in  the  embryonic  history  of  the  Vertebrata. 
But  it  must  be  remembered  that  the  science  of  com- 
parative embryology  extends  to  each  of  the  other  three 
great  branches  of  the  tree  of  life,  where  these  take 
their  origin,  through  the  worms,  from  the  still  lower, 
or  gastraea,  forms.  And  in  each  of  these  three  great 
branches — namely,  the  Echinodermata,  the  Mollusca, 
and  the  Arthropoda — we  have  a  repetition  of  just  the 
same  kind  of  evidence  in  favour  of  continuous  descent, 
with  adaptive  modification  in  sundry  lines,  as  that 
which  I  have  thus  briefly  sketched  in  the  case  of  the 
Vertebrata.  The  roads  are  different,  but  the  method 
of  travelling  is  the  same.  Moreover,  when  the  em- 
bryology of  the  Worms  is  closely  studied,  the  origin 
of  these  different  roads  admits  of  being  clearly  traced. 
So  that  when  all  this  mass  of  evidence  is  taken  to- 
gether, we  cannot  wonder  that  evolutionists  should 
now  regard  the  science  of  comparative  embryology  as 
the  principal  witness  to  their  theory. 


CHAPTER   V. 

PALEONTOLOGY. 

THE  present  Chapter  will  be  devoted  to  a  con- 
sideration of  the  evidence  of  organic  evolution 
which  has  been  furnished  by  the  researches  of  geo- 
logists. On  account  of  its  direct  or  historical  nature, 
this  branch  of  evidence  is  popularly  regarded  as  the 
most  important — so  much  so,  indeed,  that  in  the 
opinion  of  most  educated  persons  the  whole  doctrine 
of  organic  evolution  must  stand  or  fall  according  to 
the  so-called  "  testimony  of  the  rocks."  Now,  without 
at  all  denying  the  peculiar  importance  of  this  line  of 
evidence,  I  must  begin  by  remarking  that  it  does  not 
present  the  denominating  importance  which  popular 
judgment  assigns  to  it.  For  although  popular  judg- 
ment is  right  in  regarding  the  testimony  of  the  rocks 
as  of  the  nature  of  a  history,  this  judgment,  as  a  rule, 
is  very  inadequately  acquainted  with  the  great  imper- 
fections of  that  history.  Knowing  in  a  general  way 
what  magnificent  advances  the  science  of  geology  has 
made  during  the  present  century,  the  public  mind  is 
more  or  less  imbued  with  the  notion,  that  because 
we  now  possess  a  tolerably  complete  record  of  the 
chronological  succession  of  geological  formations,  we 
must  therefore  possess  a  correspondingly  complete 


Paleontology.  157 

record  of  the  chronological  succession  of  the  forms  of 
life  which  from  time  to  time  have  peopled  the  globe. 
Now  in  one  sense  this  notion  is  partly  true,  but  in 
another  sense  it  is  profoundly  false.  It  is  partly  true 
if  we  have  regard  only  to  those  larger  divisions  of 
the  vegetable  or  animal  kingdoms  which  naturalists 
designate  by  the  terms  classes  and  orders.  But  the 
notion  becomes  progressively  more  untrue  when  it  is 
applied  to  families  and  genera,  while  it  is  most  of  all 
untrue  when  applied  to  species.  That  this  must  be  so 
may  be  rendered  apparent  by  two  considerations. 

In  the  first  place,  it  does  not  follow  that  because 
we  have  a  tolerably  complete  record  of  the  succession 
of  geological  formations,  we  have  therefore  any 
correspondingly  complete  record  of  their  fossiliferous 
contents.  The  work  of  determining  the  relative  ages 
of  the  rocks  does  not  require  that  every  cubic  mile  of 
the  earth's  surface  should  be  separately  examined,  in 
order  to  find  all  the  different  fossils  which  it  may 
contain.  Were  this  the  case,  we  should  hitherto  have 
made  but  very  small  progress  in  our  reading  of  the 
testimony  of  the  rocks.  The  relative  ages  of  the 
rocks  are  determined  by  broad  comparative  surveys 
over  extensive  areas  ;  and  although  the  identification 
of  widely  separated  deposits  is  often  greatly  assisted 
by  a  study  of  their  fossiliferous  contents,  the  mere 
pricking  of  a  continent  here  and  there  is  all  that  is 
required  for  this  purpose.  Hence,  the  accuracy  of 
our  information  touching  the  relative  ages  of  geo- 
logical strata  does  not  depend  upon — and,  therefore, 
does  not  betoken — any  equivalent  accuracy  of  know^ 
ledge  touching  the  fossiliferous  material  which  these 
strata  may  at  the  present  time  actually  contain.  And, 


158          Darwin,  and  after  Darwin. 

as  we  well  know,  the  opportunities  which  the  geo- 
logist has  of  discovering  fossils  are  extremely  limited, 
if  we  consider  these  opportunities  in  relation  to  the 
area  of  geological  formations.  The  larger  portion  of 
the  earth's  surface  is  buried  beneath  the  sea ;  and 
much  the  larger  portion  of  the  fossiliferous  deposits 
on  shore  are  no  less  hopelessly  buried  beneath  the 
land.  Therefore  it  is  only  upon  the  fractional  portion 
of  the  earth's  surface  which  at  the  present  time 
happens  to  be  actually  exposed  to  his  view  that  the 
geologist  is  able  to  prosecute  his  search  for  fossils. 
But  even  here  how  miserably  inadequate  this  search 
has  hitherto  been  !  With  the  exception  of  a  scratch 
or  two  in  the  continents  of  Asia  and  America, 
together  with  a  somewhat  larger  number  of  similar 
scratches  over  the  continent  of  Europe,  even  that 
comparatively  small  portion  of  the  earth's  surface 
which  is  available  for  the  purpose  has  been  hitherto 
quite  unexplored  by  the  palaeontologist.  How  enor- 
mously rich  a  store  of  material  remains  to  be 
unearthed  by  the  future  scratchings  of  this  surface, 
we  may  dimly  surmise  from  the  astonishing  world  of 
bygone  life  which  is  now  being  revealed  in  the  newly 
discovered  fossiliferous  deposits  on  the  continent  of 
America. 

But,  besides  all  this,  we  must  remember,  in  the 
second  place,  that  all  the  fossiliferous  deposits  in  the 
world,  even  if  they  could  be  thoroughly  explored, 
would  still  prove  highly  imperfect,  considered  as  a 
history  of  extinct  forms  of  life.  In  order  that  many 
of  these  forms  should  have  been  preserved  as  fossils, 
it  is  necessary  that  they  should  have  died  upon  a 
surface  neither  too  hard  nor  too  soft  to  admit  of  their 


Paleontology.  159 

leaving  an  impression  ;  that  this  surface  should 
afterwards  have  hardened  sufficiently  to  retain  the 
impression  ;  that  it  should  then  have  been  protected 
from  the  erosion  of  water,  as  well  as  from  the  dis- 
integrating influence  of  the  air  ;  and  yet  that  it  should 
not  have  sunk  far  enough  beneath  the  surface  to  have 
come  within  the  no  less  disintegrating  influence  of 
subterranean  heat.  Remembering  thus,  as  a  general 
rule,  how  many  conditions  require  to  have  met  before 
a  fossil  can  have  been  both  formed  and  preserved, 
we  must  conclude  that  the  geological  record  is  pro- 
bably as  imperfect  in  itself  as  are  our  opportunities  of 
reading  even  the  little  that  has  been  recorded.  If  we 
speak  of  it  as  a  history  of  the  succession  of  life  upon 
the  planet,  we  must  allow,  on  the  one  hand,  that  it  is 
a  history  which  merits  the  name  of  a  "  chapter  of 
accidents";  and,  on  the  other  hand,  that  during  the 
whole  course  of  its  compilation  pages  were  being 
destroyed  as  fast  as  others  were  being  formed,  while 
even  of  those  that  remain  it  is  only  a  word,  a  line,  or 
at  most  a  short  paragraph  her"  and  there,  that  we  are 
permitted  to  see.  With  so  fragmentary  a  record  as 
this  to  study,  I  do  not  think  it  is  too  much  to  say 
that  no  conclusions  can  be  fairly  based  upon  it, 
merely  from  the  absence  of  testimony.  Only  if  the 
testimony  were  positively  opposed  to  the  theory  of 
descent,  could  any  argument  be  fairly  raised  against 
that  theory  on  the  grounds  of  this  testimony.  In 
other  words,  if  any  of  the  fossils  hitherto  discovered 
prove  the  order  of  succession  to  have  been  incom- 
patible with  the  theory  of  genetic  descent,  then  the 
record  may  fairly  be  adduced  in  argument,  because 
we  should  then  be  in  possession  of  definite  information 


160          Darwin,  and  after  Darwin. 

of  a  positive  kind,  instead  of  a  mere  absence  of  infor- 
mation of  any  kind.  But  if  the  adverse  argument 
reaches  only  to  the  extent  of  maintaining  that  the 
geological  record  does  not  furnish  us  with  so  com- 
plete a  series  of  "  connecting  links  "  as  we  might  have 
expected,  then,  I  think,  the  argument  is  futile.  Even 
in  the  case  of  human  histories,  written  with  the  inten- 
tional purpose  of  conveying  information,  it  is  an 
unsafe  thing  to  infer  the  non-occurrence  of  an  event 
from  a  mere  silence  of  the  historian — and  this  espe- 
cially in  matters  of  comparatively  small  detail,  such 
as  would  correspond  (in  the  present  analogy)  to  the 
occurrence  of  species  and  genera  as  connecting  links. 
And,  of  course,  if  the  history  had  only  come  down  to 
us  in  fragments,  no  one  would  attach  any  importance 
at  all  to  what  might  have  been  only  the  apparent 
silence  of  the  historian. 

In  view,  then,  of  the  unfortunate  imperfection  of 
the  geological  record  per  se,  as  well  as  of  the  no  less 
unfortunate  limitation  of  our  means  of  reading  even 
so  much  of  the  record  as  has  come  down  to  us,  I 
conclude  that  this  record  can  only  be  fairly  used 
in  two  ways.  It  may  fairly  be  examined  for 
positive  testimony  against  the  theory  of  descent,  or 
for  proof  of  the  presence  of  organic  remains  of  a 
high  order  of  development  in  a  low  level  of  strata. 
And  it  may  be  fairly  examined  for  negative 
testimony,  or  for  the  absence  of  connecting  links, 
if  the  search  be  confined  to  the  larger  taxonomic 
divisions  of  the  fauna  and  flora  of  the  world.  The 
more  minute  these  divisions,  the  more  restricted  must 
have  been  the  areas  of  their  origin,  and  hence  the 
less  likelihood  of  their  having  been  preserved  in  the 


Paleontology.  1 6 1 

fossil  state,  or  of  our  rinding  them  even  if  they 
have  been.  Therefore,  if  the  theory  of  evolution  is 
true,  we  ought  not  to  expect  from  the  geological 
record  a  full  history  of  specific  changes  in  any  but 
at  most  a  comparatively  small  number  of  instances, 
where  local  circumstances  happen  to  have  been 
favourable  for  the  writing  and  preservation  of  such  a 
history.  But  we  might  reasonably  expect  to  find  a 
general  concurrence  of  geological  testimony  to  the 
larger  fact — namely,  of  there  having  been  throughout 
all  geological  time  a  uniform  progression  as  regards 
the  larger  taxonomic  divisions.  And,  as  I  will  next 
proceed  to  show,  this  is,  in  a  general  way,  what  we  do 
find,  although  not  altogether  without  some  important 
exceptions,  with  which  I  shall  deal  in  an  Appendix. 

There  is  no  positive  proof  against  the  theory  of 
descent  to  be  drawn  from  a  study  of  palaeontology,  or 
proof  of  the  presence  of  any  kind  of  fossils  in  strata 
where  the  fact  of  their  presence  is  incompatible  with 
the  theory  of  evolution.  On  the  other  hand,  there  is 
an  enormous  body  of  uniform  evidence  to  prove  two 
general  facts  of  the  highest  importance  in  the  present 
connexion.  The  first  of  these  general  facts  is,  that  an 
increase  in  the  diversity  of  types  both  of  plants  and 
animals  has  been  constant  and  progressive  from  the 
earliest  to  the  latest  times,  as  we  should  anticipate  that 
it  must  have  been  on  the  theory  of  descent  in  ever- 
ramifying  lines  of  pedigree.  And  the  second  general 
fact  is,  that  through  all  these  branching  lines  of  ever- 
multiplying  types,  from  the  first  appearance  of  each 
of  them  to  their  latest  known  conditions,  there  is 
overwhelming  evidence  of  one  great  law  of  organic 
nature — the  law  of  gradual  advance  from  the  general 

*  M 


1 62          Darwin,  and  after  Darwin. 

to  the  special,  from  the  low  to  the  high,  from  the 
simple  to  the  complex. 

Now,  the  importance  of  these  large  and  general 
facts  in  the  present  connexion  must  be  at  once 
apparent ;  but  it  may  perhaps  be  rendered  more  so  if 
we  try  to  imagine  how  the  case  would  have  stood 
supposing  geological  investigation  to  have  yielded  in 
this  matter  an  opposite  result,  or  even  so  much  as  an 
equivocal  result.  If  it  had  yielded  an  opposite  result, 
if  the  lower  geological  formations  were  found  to 
contain  as  many,  as  diverse,  and  as  highly  organized 
types  as  the  later  geological  formations,  clearly  there 
would  have  been  no  room  at  all  for  any  theory  of  pro- 
gressive evolution.  And,  by  parity  of  reasoning,  in 
whatever  degree  such  a  state  of  matters  were  found  to 
prevail,  in  that  degree  would  the  theory  in  question 
have  been  discredited.  But  seeing  that  these  opposite 
principles  do  not  prevail  in  any  (relatively  speaking) 
considerable  degree l,  we  have  so  far  positive  testimony 
of  the  largest  and  most  massive  character  in  favour  of 
this  theory.  For  while  all  these  large  and  general 
facts  are  very  much  what  they  ought  to  be  according 
to  this  theory,  they  cannot  be  held  to  lend  any 
support  at  all  to  the  rival  theory.  In  other  words,  it 
is  clearly  no  essential  part  of  the  theory  of  special 
creation  that  species  should  everywhere  exhibit  this 
gradual  multiplication  as  to  number,  coupled  with  a 
gradual  diversification  and  general  elevation  of  types, 
in  all  the  growing  branches  of  the  tree  of  life.  No 
one  could  adopt  seriously  the  jocular  lines  of  Burns, 
to  the  effect  that  the  Creator  required  to  practise  his 

1  For  objections  which  may  be  brought  against  this  and  similar 
statements,  see  the  Appendix. 


Paleontology. 


163 


Efochs  and  Formations. 

Fauna!  Characters. 

S3 

POST-PLIOCENE. 
Glacial  Period. 

Man.     Mammalia  principally  of  living 
species.     Mollusca  exclusively  recent. 

TERTIAF 

PLIOCENE,  3,000  feet. 

Mammalia  principally  of  recent  genera 
—  living  species  rare.    Mollusca  very 
modern. 

INOZOIC  or 

MIOCENE,  4,000  ft. 
OLIGOCENE,  8,000  ft. 

Mammalia  principally  of  living  families  ; 
extinct  genera  numerous  ;  species  all 
extinct.     Mollusca  largely   of   recent 
species. 

2 

EOCENE,  10,000  ft. 

Mammalia  with  numerous  extinct  fam- 
ilies and  orders;  all  the  species  and 
most  of  the  genera  extinct.    Modern 
type  Shell-Fish. 

LARAMIE,  4,000  ft. 

Passage  Beds. 

1 

CRETACEOUS,  12,000  ft. 
Chalk. 

Dinosaurian  (bird-like)  Reptiles  ;  Ptero- 
dactyls    (flying     Reptiles);      toothed 
Birds;    earliest  Snake  ;  l.ony  Fishes; 
Crocodiles;  Turtles;  Ammonites. 

CD 

JURASSIC,  6,000  ft. 
Oolite. 
Lias. 

Earliest  Birds  ;  giant  Reptiles  (Ichthyo- 
saurs,  Dinosaurs,  Pterodactyls);  Am- 
monites; Clam-and  Snail-Shells  very 
abundant;    decline    of   Brachiopods; 
Butterfly. 

I 

TRIAS,  5,000  ft. 
New  Red  Sandstone. 

First  Mammalian  (Marsupial);  2-gilled 
Cephalopods    (Cuttle-Fishes,    Belem- 
nites);  reptilian  Foot-Prints. 

PERMIAN,  5,000  ft. 

Earliest  true  Reptiles. 

^ 
< 

CARBONIFEROUS, 
26,000  ft. 
Coal. 

Earliest  Amphibian  (Labyrinthodont)  ; 
extinction  of  Trilobites  ;    first  Cray- 
fish;   Beetles;    Cockroaches;    Centi- 
pedes ;  Spiders. 

a. 

H 

DEVONIAN,  18,000  ft. 
Old  Red  Sandstone. 

Cartilaginous  and  Ganoid  Fishes;  ear- 
liest    land     (snail)     and     freshwater 
Shells;   Shell-Fish  abundant;  decline 
of  Trilobites  ;  May-flies;  Crab. 

PALEOZO 

SILURIAN,  33,000  ft. 

Earliest   Fish  ;    the  first  Air-Breathers 
(Insect,  Scorpion);  Brachiopods  and 
4-gilled  Cephalopods  very  abundant; 
Trilobites  ;  Corals  ;  Graptolites. 

CAMBRIAN,  24000  ft. 

Trilobites  ;  Brachiopod  Mollusks. 

< 

f 

ARCHAEAN,  30,000  ft. 
Huronian. 
Laurentian. 

Eozoon  (probably  not  a  fossil). 

PRIMEVAL, 

Non-sedimentary. 

M  2 


164          Darwin,  and  after  Darwin. 

prentice  hand  on  lower  types  before  advancing  to  the 
formation  of  higher.  Yet,  without  some  such  assump- 
tion, it  would  be  impossible  to  explain,  on  the  theory 
of  independent  creations,  why  there  should  have  been 
this  gradual  advance  from  the  few  to  the  many,  from 
the  general  to  the  special,  from  the  low  to  the  high. 

I  submit,  then,  that  so  far  as  the  largest  and  most 
general  principles  in  the  matter  of  palaeontology  are 
concerned,  we  have  about  as  strong  and  massive  a 
body  of  evidence  as  we  could  reasonably  expect  this 
branch  of  science  to  yield  ;  for  it  is  at  once  enormous 
in  amount  and  positive  in  character.  Therefore,  if 
I  do  not  further  enlarge  upon  the  evidence  which 
we  here  have,  as  it  were  en  masse,  it  is  only  because 
I  do  not  feel  that  any  words  could  add  to  its  obvious 
significance.  It  may  best  be  allowed  to  speak  for  itself 
in  the  millions  of  facts  which  are  condensed  in  this 
tabular  statement  of  the  order  of  succession  of  all  the 
known  forms  of  animal  life,  as  presented  by  the 
eminent  palaeontologist,  Professor  Cope  l. 

Or,  taking  a  still  more  general  survey,  this  tabular 
statement  may  be  still  further  condensed,  and  pre- 
sented in  a  diagrammatic  form,  as  it  has  been  by  another 
eminent  American  palaeontologist,  Prof.  Le  Conte,  in 
his  excellent  little  treatise  on  Evolution  and  its 
Relations  to  Religious  Thought.  The  following  is 
his  diagrammatic  representation,  with  his  remarks 
thereon. 

\\hen  each  ruling  class  declined  in  importance,  it  did  not 
perish,  but  continued  in  a  subordinate  position.  Thus,  the 
whole  organic  kingdom  became  not  only  higher  and  higher  in 
its  highest  forms,  but  also  more  and  more  complex  in  its  struc- 

1  For  difficulties  and  objections,  see  Appendix. 


Paleontology. 


165 


ture  and  in  the  interaction  of  its  correlated  parts.  The  whole 
process  and  its  result  is  roughly  represented  in  the  accompanying 
diagram,  in  which  A  B  represents  the  course  of  geological  time, 
and  the  curve,  the  rise,  culmination,  and  decline  of  successive 
dominant  classes. 


FIG.  59. — Diagram  of  Geological  Succession  of  the  Classes  of  the 
Animal  Kingdom.     (After  Le  Conte.) 

I  will  here  leave  the  evidence  which  is  thus  yielded 
by  the  most  general  principles  that  have  been  esta- 
blished by  the  science  of  palaeontology ;  and  I  will 
devote  the  rest  of  this  chapter  to  a  detailed  con- 
sideration of  a  few  highly  special  lines  of  evidence. 
By  thus  suddenly  passing  from  one  extreme  to  the 
other,  I  hope  to  convey  the  best  idea  that  can  be 
conveyed  within  a  brief  compass  of  the  minuteness,  as 
well  as  the  extent,  of  the  testimony  which  is  furnished 
by  the  rocks. 

When  Darwin  first  published  his  Origin  of  Species, 
adverse  critics  fastened  upon  the  "  missing-link  "  argu- 
ment as  the  strongest  that  they  could  bring  against 
the  theory  of  descent.  Although  Darwin  had  himself 
strongly  insisted  on  the  imperfection  of  the  geological 
record,  and  the  consequent  precariousness  of  any  ne- 
gative conclusions  raised  upon  it,  these  crit'  - ;  main- 
tained that  he  was  making  too  great  a  demand  upon  the 
argument  from  ignorance — that,  even  allowing  for  the 
imperfection  of  the  record,  they  would  certainly  have 
expected  at  least  a  few  cases  of  testimony  to  specific 
transmutation.  For,  they  urged  in  effect,  looking  to 


i66  Darwin,  and  after  Darwin. 

the  enormous  profusion  of  the  extinct  species  on  the 
one  hand,  and  to  the  immense  number  of  known 
fossils  on  the  other,  it  was  incredible  that  no  satis- 
factory instances  of  specific  transmutation  should  ever 
have  been  brought  to  light,  if  such  transmutation  had 
ever  occurred  in  the  universal  manner  which  the  theory 
was  bound  to  suppose.  But  since  Darwin  first 
published  his  great  work  palaeontologists  have  been 
very  active  in  discovering  and  exploring  fossiliferous 
beds  in  sundry  parts  of  the  world ;  and  the  result  of 
their  labours  has  been  to  supply  so  many  of  the 
previously  missing  links  that  the  voice  of  competent 
criticism  in  this  matter  has  now  been  well-nigh  silenced. 
Indeed,  the  material  thus  furnished  to  an  advocate  of 
evolution  at  the  present  time  is  so  abundant  that  his 
principal  difficulty  is  to  select  his  samples.  I  think, 
however,  that  the  most  satisfactory  result  will  be 
gained  if  I  restrict  my  exposition  to  a  minute  account 
of  some  few  series  of  connecting  links,  rather  than  if 
I  were  to  take  a  more  general  survey  of  a  larger 
number.  I  will,  therefore,  confine  the  survey  to  the 
animal  kingdom,  and  there  mention  only  some  of  the 
cases  which  have  yielded  well-detailed  proof  of  con- 
tinuous differentiation. 

It  is  obvious  that  the  parts  of  animals  most  likely 
to  have  been  preserved  in  such  a  continuous  series  of 
fossils  as  the  present  line  of  evidence  requires,  would 
have  been  the  hard  parts.  These  are  horns,  bones, 
teeth,  and  shells.  Therefore  I  will  consider  each  of 
these  four  classes  of  structures  separately. 

Horns  wherever  they  occur,  are  found  to  be  of  high 
importance  for  purposes  of  classification.  They  are 


Paleontology. 


[67 


restricted  to  the  Ruminants,  and  appear  under  three 
different  forms  or  types  —  namely. solid,  as  in  antelopes  ; 
hollow,  as  in  sheep  ;  and  deciduous,  as  in  deer.  Now, 
in  each  of  these  divisions  we  have  a  tolerably  complete 
palaeontological  history  of  the  evolution  of  horns. 
The  early  ruminants  were  altogether  hornless  (Fig.  60). 


Fig.  60.— Skull  of  Oreodon  Culbertsoni.     (After  Leidy.) 

Then,  in  the  middle  Miocene,  the  first  antelopes  ap- 
peared with  tiny  horns  which  progressively  increased  in 
size  among  the  ever-multiplying  species  of  antelopes 
until  the  present  day.  But  it  is  in  the  deer  tribe  that  we 
meet  with  even  better  evidence  touching  the  pro- 
gressive evolution  of  horns  ;  because  here  not  only 
size,  but  shape,  is  concerned.  For  deer's  horns,  or 
antlers,  are  arborescent ;  and  hence  in  their  case  we 
have  an  opportunity  of  reading  the  history,  not  only 
of  a  progressive  growth  in  size,  but  also  of  an  increasing 
development  of  form.  Among  the  older  members  of 
the  tribe,  in  the  lower  Miocene,  there  are  no  horns  at 


1 68          Darwin,  and  after  Darwin. 

all.  In  the  mid-Miocene  we  meet  with  two-pronged 
horns  (Cervus  dicrocerus,  Figs.  61,  62,  \  nat.  size). 
Next,  in  the  upper  Miocene  (C.  matheronis,  Fig. 
63,  |  nat.  size),  and  extending  into  the  Pliocene 
(C.  pardinensts,  Fig.  64,  T\  nat.  size),  we  meet  with 
three-pronged  horns.  Then,  in  the  Pliocene  we  find  also 
four  pronged  horns  (C.  issiodorensis,  Fig.  65,  y^  nat. 
size),  leading  us  to  five-pronged  (C.  tetraceros).  Lastly, 
in  the  Forest-bed  of  Norfolk  we  meet  with  arborescent 


FIG.  61.    FIG.  62.    FIG.  63.    FIG.  64.        FIG.  65. 


The  series  is  reduced  from  Gaudry's  illustrations,  after  Farge,  Croizet, 
Jobert  and  Boyd  Dawk  ins. 

horns  (C.  Sedgwickii,  Fig.  66,  -fc  nat.  size).  The 
life-history  of  existing  stags  furnishes  a  parallel 
development  (Fig.  67),  beginning  with  a  single  horn 
(which  has  not  yet  been  found  palaeontologically), 
going  on  to  two  prongs,  three  prongs,  four  prongs,  and 
afterwards  branching. 

Coming  now  to  bones,  we  have  a  singularly  complete 
record    of  transition    from    one   type   or   pattern    of 


Paleontology. 


169 


structure  to  another  in  the  phylogenetic  history  of 
tails.    This  has  been  so  clearly  and  so  tersely  conveyed 


FIG.  67.— Successive  stages  in  the  development  of  an  existing  Deer's 
Antlers.  (After  Gaudry,  but  a  better  illustration  has  already  been 
given  on  p.  100.) 


FlG.  68. — Homocercal  Tail,  showing  (A)  external  form  and 
(B)  internal  structure. 

by  Prof.  Le  Conte,  that  I  cannot  do  better  than  quote 
his  statement. 


1 70          Darwin^  and  after  Darwin. 

It  has  long  been  noticed  that  there  are  among  fishes  two  styles 
of  tail-fins.  These  are  the  even-lobed,  or  homocercal  (Fig.  68), 
and  the  uneven-lobed,  or  heterocercal  (Fig.  69).  The  one  is 
characteristic  of  ordinary  fishes  (teleosts),  the  other  of  sharks 


FIG.  69. — Heterocercal  Tail,  showing  (A)  external  form  and 
(B)  internal  structure. 


FIG.  70. — Vertebrated  but  symmetrical  fin  ;diphycercal),  showing 
(A)  external  form  and  ^B)  internal  structure. 

and  some  other  orders.  In  structure  the  difference  is  even  more 
fundamental  than  in  form.  In  the  former  style  the  backbone 
stops  abruptly  in  a  series  of  short,  enlarged  joints,  and  thence 
sends  off  rays  to  form  the  tail-fin  (Fig.  68) ;  in  the  latter  the 


Paleontology. 


backbone  runs  through  the  fin  to  its  very  point,  growing  slen- 
derer by  degrees,  and  giving  off  rays  above  and  below  from  each 
joint,  but  the  rays  on  the  lower  side  are  much  longer  (Fig.  69). 
This  type  of  fin  is,  therefore,  vertebrated,  the  other  non- 
vertebrated.  Figs.  68  and  69  show  these  two  types  in  form  and 
structure.  But  there  is  still  another  type  found  only  in  the  low- 
est and  most  generalized  forms  of  fishes.  In  these  the  tail-fin  is 
vertebrated  and  yet  symmetrical.  This  type  is  shown  in  Fig.  70. 


FlG.  71.— Tail  of  Archaoptoyx. 
A  indicates  origin  of  simply- 
jointed  tail. 


FIG.  72. — Tail  of  modern  Bird. 
The  numerals  indicate  the  fore- 
shortened, enlarged,  and  con- 
solidated joints ;  f,  terminal 
segment  of  the  vertebral  column ; 
D,  shafts  of  feathers. 


Now,  in  the  development  of  a  teleost  fish  (Fig.  68),  as  has 
been  shown  by  Alexander  Agassiz,  the  tail-fin  is  first  like  Fig. 
70 ;  then  becomes  heterocercal,  like  Fig.  69 ;  and,  finally,  be- 
comes homocercal  like  Fig.  68.  Why  so  ?  Not  because  there 
is  any  special  advantage  in  this  succession  of  forms ;  for  the 
changes  take  place  either  in  the  egg  or  else  in  very  early  em- 
bryonic states.  The  answer  is  found  in  the  fact  that  this  is  the 
order  of  change  in  the  phylogenetic  series.  The  earliest  fish-tails 
were  either  like  Fig.  69  or  Fig.  70 ;  never  like  Fig.  68.  The 


72  Darwin,  and  after  Darwin. 


FlG.  Il.—Archaopteryx  mactira,  restored,  \  nat.  size.     (After 
Flower.)     The  section  of  the  tail  is  copied  from  Owen,  nat.  size. 


Palaeontology.  173 

earliest  of  all  were  almost  certainly  like  Fig.  70 ;  then  they  be- 
came like  Fig.  69 ;  and,  finally,  only  much  later  in  geological 
history  (Jurassic  or  Cretaceous),  they  became  like  Fig.  68.  This 
order  of  change  is  still  retained  in  the  embryonic  development 
of  the  last  introduced  and  most  specialized  order  of  existing 
fishes.  The  family  history  is  repeated  in  the  individual  history. 
Similar  changes  have  taken  place  in  the  form  and  structure  of 
birds'  tails.  The  earliest  bird  known — the  Jurassic  Archceo- 
pteryx—\i?i&  a  long  reptilian  tail  of  twenty-one  joints,  each  joint 
bearing  a  feather  on  each  side,  right  and  left  (Fig.  71)  :  [see  also 
Fig-  73J-  In  the  typical  modern  bird,  on  the  contrary,  the  tail- 
joints  are  diminished  in  number,  shortened  up,  and  enlarged, 
and  give  out  long  feathers,  fan-like,  to  form  the  so-ca'.led  tail 
(Fig.  72).  The  Archceoptcryx'  tail  is  vertebrated^  the  typical 
bird's  non-vertebr<i1ed.  This  shortening  up  of  the  tail  did  not 
take  place  at  once,  but  gradually.  The  Cretaceous  birds,  inter- 
mediate in  time,  had  tails  intermediate  in  structure.  The  Hes- 
perornis  of  Marsh  had  twelve  joints.  At  first— in  Jurassic  strata— 
the  tail  is  fully  a  half  of  the  whole  vertebral  column.  It  then  grad- 
ually shortens  up  until  it  becomes  the  aborted  organ  of  typical 
modern  birds.  Now,  in  embryonic  development,  the  tail  of  the 
modern  typical  bird  passes  through  all  these  stages.  At  first  the 
tail  is  nearly  one  half  the  whole  vertebral  column  ;  then,  as  de- 
velopment goes  on,  while  the  rest  of  the  body  grows,  the  growth 
of  the  tail  stops,  and  thus  finally  becomes  the  aborted  organ  we 
now  find.  The  ontogeny  still  passes  through  the  stages  of  the 
phylogeny.  The  same  is  true  of  all  tailless  animals. 

The  extinct  Archczopteryx  above  alluded  to  presents 
throughout  its  whole  organization  a  most  interesting 
assemblage  of  "  generalized  characters."  For  example, 
its  teeth,  and  its  still  unreduced  digits  of  the  wings 
(which,  like  those  of  the  feet,  are  covered  with  scales), 
refer  us,  with  almost  as  much  force  as  does  the  verte- 
brated  tail,  to  the  Sauropsidian  type — or  the  trunk 
from  which  birds  and  reptiles  have  diverged. 

We  will  next  consider  the  palaeontological  evidence 


174          Darwin,  and  after  Darwin. 


Pa  Ice  onto  logy.  1 7  5 

which  we  now  possess  of  the  evolution  of  mammalian 
limbs,  with  special  reference  to  the  hoofed  animals, 


where   this    line   of   evidence    happens   to   be    most 
complete. 

I  may  best  begin  by  describing  the  bones  as  these 


176  Darwin,  and  after  Darwin. 

occur  in  the  sundry  branches  of  the  mammalian  type 
now  living.  As  we  shall  presently  see,  the  modi- 
fications which  the  limbs  have  undergone  in  these 


•4  *  £ 


sundry  branches  chiefly  consist  in  the  suppression  of 
some  parts  and  the  exaggerated  development  of  others. 
But,  by  comparing  all  mammalian  limbs  together,  it  is 
easy  to  obtain  a  generalized  type  of  mammalian  limbs 


177 

which  in  actual  life  is  perhaps  most  nearly  conformed 
to  in  the  case  of  bears.     I  will  therefore  choose  the 


bear  for  the  purpose  of  briefly  expounding  the  bones 
of  mammalian  limbs  in  general — merely  asking  it  to  be 


178          Darwin,  and  after  Darwin. 

understood,  that  although  in  the  case  of  many  other 
mammalia  some  of  these  bones  may  be  dwindled  or 
altogether  absent,  while  others  may  be  greatly  ex- 
aggerated as  to  relative  size,  in  no  case  do  any 
additional  bones  appear. 

On  looking,  then,  at  the  skeleton  of  a  bear  (Fig.  74), 
the  first  thing  to  observe  is  that  there  is  a  perfect  serial 
homology  between  the  bones  of  the  hind  legs  and  of 
the  fore  legs.  The  thigh-bone,  or  femur,  corresponds 
to  the  shoulder-bone,  or  humerus  ;  the  two  shank 
bones  (tibia  and  fibula)  correspond  to  the  two  arm-bones 
(radius  and  ulna) ;  the  many  little  ankle-bones  (tarsals) 
correspond  to  the  many  little  wrist-bones  (carpals)  ; 
the  foot-bones  (meta-tarsals)  correspond  to  the  hand- 
bones  (meta-carpals) ;  and,  lastly,  the  bones  of  each 
of  the  toes  correspond  to  those  of  each  of  the  fingers. 

The  next  thing  to  observe  is,  that  the  disposition  of 
bones  in  the  case  of  the  bear  is  such  that  the  animal 
walks  in  the  way  that  has  been  called  plantigrade. 
That  is  to  say,  all  the  bones  of  the  fingers,  as  well  as 
those  of  the  toes,  feet,  and  ankles,  rest  upon  the  ground, 
or  help  to  constitute  the  "  soles."  Our  own  feet  are 
constructed  on  a  closely  similar  pattern.  But  in  the 
majority  of  living  mammalian  forms  this  is  not  the 
case.  For  the  majority  of  mammals  are  what  has 
been  called  digitigrade.  That  is  to  say,  the  bones  of 
the  limb  are  so  disposed  that  both  the  foot  and  hand 
bones,  and  therefore  also  the  ankle  and  wrist,  are 
removed  from  the  ground  altogether,  so  that  the 
animal  walks  exclusively  upon  its  toes  and  fingers — as 
in  the  case  of  this  skeleton  (Fig.  75),  which  is  the  skele- 
ton of  a  lion.  The  next  figures  display  a  series  of 
limbs,  showing  the  progressive  passage  of  a  completely 


Palaeontology.  1 79 

plantigrade  into  a  highly  digitigrade  type — the 
curved  lines  of  connexion  serving  to  indicate  the 
homologous  bones  (Figs.  76,  77). 

I  will  now  proceed  to  detail  the  history  of  mammalian 
limbs,  as  this  has  been  recorded  for  us  in  fossil  remains. 

The  most  generalized  or  primitive  types  of  limb 
hitherto  discovered  in  any  vertebrated  animal  above 


/    '^-^   ^-'  *<SL^/  s^.^J/ 

<Q>  0)0^0 

mm 


M  O  Q  @  #  ° 

O  <3  G>  (if   j- 

0    Q    O     „. 

v   o  o    JL 

O     JJt 

Pf 

A  B 

FlG.  78. — A,  posterior  limb  of  Baptanodon  discus.  (After  Marsh.)  F, 
thigh-bone;  I  to  VI,  undifferentiated  bones  of  the  leg  and  foot.  B, 
anterior  limb  of  Chelydra  serpentina.  (After  Gcgenbanr.)  U  and  R, 
bones  of  the  fore-arm ;  I  to  V,  fully  differentiated  bones  of  the  hand, 
following  those  of  the  wrist. 

the  class  of  fishes,  are  those  which  are  met  with  in 
some  of  the  extinct  aquatic  reptiles.  Here,  for 
instance,  is  a  diagram  of  the  left  hind  limb  of 
Baptanodon  discus  (Fig.  78).  It  has  six  rows  of  little 
symmetrical  bones  springing  from  a  leg-like  origin. 
N  2 


180          Darwin,  and  after  Darwin. 


But  the  whole  structure  resembles  the  fin  of  a  fish 
about  as  nearly  as  it  does  the  leg  of  a  mammal.     For 
not  only  are  there  six  rows 
,  of  bones,    instead  of  five, 

suggestive  of  the  numerous 
rays  which  characterise  the 
fin  of  a  fish  ;  but  the  struc- 
ture as  a  whole,  having 
been  covered  over  with 
blubber  and  skin,  was 
throughout  flexible  and 
unjointed — thus  in  func- 
tion, even  more  than  in 
structure,  resembling  a  fin. 
In  this  respect,  also,  it 
must  have  resembled  the 
paddle  of  a  whale  (see 
Fig.  79) ;  but  of  course  the 
great  difference  will  be 
noted,  that  the  paddle 
of  a  whale  reveals  the 

dwindled  though  still  clearly  typical  bones  of  a  true 
mammalian  limb  ;  so  that  although  in  outward  form 
and  function  these  two  paddles  are  alike,  their  inward 
structure  clearly  shows  that  while  the  one  testifies  to 
the  absence  of  evolution,  the  other  testifies  to  the 
presence  of  degeneration.  If  the  paddle  of  Baptanodon 
had  occurred  in  a  whale,  or  the  paddle  of  a  whale  had 
occurred  in  Baptanodon,  either  fact  would  in  itself  have 
been  well-nigh  destructive  of  the  whole  theory  of 
evolution. 

Such,  then,  is  the  most  generalized  as  it  is  the  most 
ancient  type  of  vertebrate  limb  above  the  class  of 


FIG.  79.— Paddle  of  a  Whale. 


Paleontology.  1 8 1 

fishes.  Obviously  it  is  a  type  suited  only  to  aquatic 
life.  Consequently,  when  aquatic  Vertebrata  began  to 
become  terrestrial,  the  type  would  have  needed  modi- 
fication in  order  to  serve  for  terrestrial  locomotion.  In 
particular,  it  would  have  needed  to  gain  in  consolida- 
tion and  in  firmness,  which  means  that  it  would  have 
needed  also  to  become  jointed.  Accordingly,  we  find 
that  this  archaic  type  gave  place  in  land -reptiles  to 
the  exigencies  of  these  requirements.  Here  for  ex- 
ample is  a  diagram,  copied  from  Gegenbaur,  of  the  right 
fore-foot  of  Chelydra  serpentina  (Fig.  78).  As  com- 
pared with  the  homologous  limb  of  its  purely  aquatic 
predecessor,  there  is  to  be  noticed  the  disappearance 
of  one  of  the  six  rows  of  small  bones,  a  confluence  of 
some  of  the  remainder  in  the  other  five  rows,  a  dupli- 
cation of  the  arm-bone  into  a  radius  and  ulna,  in 
order  to  admit  of  jointed  rotation  of  the  hand,  and  a 
general  disposition  of  the  small  bones  below  these 
arm-bones,  which  clearly  foreshadows  the  joint  of  the 
wrist.  Indeed,  in  this  fore-foot  of  Chelydra,  a  child 
could  trace  all  the  principal  homologies  of  the  mam- 
malian counterpart,  growing,  like  the  next  stage  in  a 
dissolving  view,  out  of  the  primitive  paddle  of  Bapta- 
nodon — namely,  first  the  radius  and  ulna,  next  the 
carpals,  then  the  meta-carpals,  and,  lastly,  the  three 
phalanges  in  each  of  the  five  digits. 

Such  a  type  of  foot  no  doubt  admirably  meets  the 
requirements  of  slow  reptilian  locomotion  over  swampy 
ground.  But  for  anything  like  rapid  locomotion  over 
hard  and  uneven  ground,  greater  modifications  would 
be  needed.  Such  modifications,  however,  need  not 
be  other  in  kind  :  it  is  enough  that  they  should  con- 
tinue in  the  same  line  of  advance,  so  as  to  reach  a 


1 82  Darwin,  and  after  Darwin. 

higher  degree  of  firmness,  combined  with  better  joints. 
Accordingly  we  find  that  this  took  place,  not  indeed 
among  reptiles,  whose  habits  of  cold-blooded  life  have 
not  changed,  but  among  their  warm-blooded  de- 
scendants, the  mammals.  Moreover,  when  we  examine 
the  whole  mammalian  series,  we  find  that  the  required 
modifications  must  have  taken  place  in  slightly  differ- 
ent ways  in  three  lines  of  descent  simultaneously.  We 
have  first  the  plantigrade  and  digitigrade  modifications 
already  mentioned  (pp.  178,  179).  Of  these  the 
plantigrade  walking  entailed  least  change,  because 
most  resembling  the  ancestral  or  lizard-like  mode  of 
progression.  All  that  was  here  needed  was  a  general 
improvement  as  to  relative  lengths  of  bones,  with 
greater  consolidation  and  greater  flexibility  of  joints. 
Therefore  I  need  not  say  anything  more  about  the 
plantigrade  division.  But  the  digitigrade  modification 
necessitated  a  change  of  structural  plan,  to  the  extent 
of  raising  the  wrist  and  ankle  joints  off  the  ground,  so 
as  to  make  the  quadruped  walk  on  its  fingers  and  toes. 
We  meet  with  an  interesting  case  of  this  transition 
in  the  existing  hare,  which  while  at  rest  supports 
itself  on  the  whole  hind  foot  after  the  manner  of  a 
plantigrade  animal,  but  when  running  does  so  upon 
the  ends  of  its  toes,  after  the  manner  of  a  digitigrade 
animal. 

It  is  of  importance  for  us  to  note  that  this  transi- 
tion from  the  original  plantigrade  to  the  more  recent 
digitigrade  type,  has  been  carried  out  on  two  slightly 
different  plans  in  two  different  lines  of  mamma- 
lian descent.  The  hoofed  mammals— which  are  all 
digitigrade — are  sub-classified  as  artiodactyls  and 
perissodactyls,  i.  e.  even-loed  and  odd-toed.  Now, 


Paleontology.  m      183 

whether  an  animal  has  an  even  or  an  odd  number 
of  toes  may  seem  a  curiously  artificial  distinction 
on  which  to  found  so  important  a  classification 
of  the  mammalian  group.  But  if  we  look  at  the 
matter  from  a  less  empirical  and  more  intelligent 
point  of  view,  we  shall  see  that  the  alternative  of 
having  an  even  or  an  odd  number  of  toes  carries  with 
it  alternative  consequences  of  a  practically  important 
kind  to  any  animal  of  the  digitigrade  type.  For 
suppose  an  aboriginal  five- toed  animal,  walking  on 
the  ends  of  its  five  toes,  to  be  called  upon  to  resign 
some  of  his  toes.  If  he  is  left  with  an  even  number, 
it  must  be  two  or  four  ;  and  in  either  case  the  animal 
would  gain  the  firmest  support  by  so  disposing  his 
toes  as  to  admit  of  the  axis  of  his  foot  passing  be- 
tween an  equal  number  of  them — whether  it  be  one  or 
two  toes  on  each  side.  On  the  other  hand,  if  our  early 
mammal  were  called  upon  to  retain  an  odd  number 
of  toes,  he  would  gain  best  support  by  adjusting 
matters  so  that  the  axis  of  his  foot  should  be  coinci- 
dent with  his  middle  toe,  whether  this  were  his  only 
toe,  or  whether  he  had  one  on  either  side  of  it. 
This  consideration  shows  that  the  classification 
into  even-toed  and  odd-toed  is  not  so  artificial  as 
it  no  doubt  at  first  sight  appears.  Let  us,  then, 
consider  the  stages  in  the  evolution  of  both  these  types 
of  feet. 

Going  back  to  the  reptile  CJielydra^  it  will  be 
observed  that  the  axis  of  the  foot  passes  down  the 
middle  toe,  which  is  therefore  supported  by  two  toes 
on  either  side  (Fig.  78).  It  may  also  be  noticed  that 
the  wrist  or  ankle  bones  do  not  interlock, either  with  one 
another  or  with  the  bones  of  the  hand  or  foot  below 


184          Darwin,  and  after  Darwin. 

them.     This,  of  course,  would  give  a  weak  foot,  suited 
to  slow  progression  over  marshy  ground — which,  as 


we  have  seen,  was  no  doubt  the  origin  of  the  mam- 
malian plantigrade  foot.  Here,  for  instance,  to  all  in- 
tents and  purposes,  is  a  similar  type  of  foot,  which 


Paleontology.  185 

belonged  to  a  very  early  mammal,  antecedent  to  the 
elephant  series,  the  horse  series,  the  rhinoceros,  the 
hog,  and,  in  short,  all  the  known  hoofed  mammalia 
(Fig.  80).  It  was  presumably  an  inhabitant  of 
swampy  ground,  slow  in  its  movements,  and  low  in 
its  intelligence. 

But  now,  as  we  have  seen,  for  more  rapid  progression 
on  hard  uneven  ground,  a  stronger  and  better  jointed 
foot  would  be  needed.  Therefore  we  find  the  bones 
of  the  wrist  and  ankle  beginning  to  interlock,  both 
among  themselves  and  also  with  those  of  the  foot  and 
hand  immediately  below  them.  Such  a  stage  of 
evolution  is  still  apparent  in  the  now  existing  elephant. 
(See  Fig.  81.) 

Next,  however,  a  still  stronger  foot  was  made  by 
the  still  further  interlocking  of  the  wrist  and  ankle 
bones,  so  that  both  the  first  and  second  rows  of  them 
were  thus  fitted  into  each  other,  as  well  as  into  the 
bones  of  the  hand  and  foot  beneath.  This  further 
modification  is  clearly  traceable  in  some  of  the  earlier 
perissodactyls,  and  occurs  in  the  majority  at  the 
present  time.  Compare,  for  example,  the  greater  in- 
terlocking and  consolidation  of  these  small  bones  in  the 
Rhinoceros  as  contrasted  with  the  Elephant  (Fig.  81). 
Moreover,  simultaneously  with  these  consolidating  im- 
provements in  the  mechanism  of  the  wrist  and  ankle 
joints,  or  possibly  at  a  somewhat  later  period,  a  reduc- 
tion in  the  number  of  digits  began  to  take  place.  This 
was  a  continuation  of  the  policy  of  consolidating  the 
foot,  analogous  to  the  dropping  out  of  the  sixth  row 
of  small  bones  in  the  paddle  of  Baptanodon.  (Fig. 
78.)  In  the  pentadactyl  plantigrade  foot  of  the  early 
mammals,  the  first  digit,  being  the  shortest,  was  th» 


1 88          Darwin,  and  after  Darwin. 

first  to  leave  the  ground,  to  dwindle,  and  finally  to 
disappear.  More  work  being  thus  thrown  on  the 
remaining  four,  they  were  strengthened  by  inter- 
locking with  the  wrist  (or  ankle)  bones  above  them,  as 
just  mentioned ;  and  also  by  being  brought  closer 
together. 

The  changes  which  followed  I  will  render  in  the 
words  of  Professor  Marsh. 

Two  kinds  of  reduction  began.  One  leading  to  the  existing 
perissodactyl  foot,  and  the  other,  apparently  later,  resulting  in  the 
artiodactyl  type.  In  the  former  the  axis  of  the  foot  remained 
in  the  middle  of  the  third  digit,  as  in  the  pentadactyl  foot-  [See 
Fig.  81.]  In  the  latter,  it  shifted  to  the  outer  side  of  this  digit, 
or  between  the  third  and  fourth  toe.  [See  Fig.  82.] 

In  the  further  reduction  of  the  perissodactyl  foot,  the  fifth 
digit,  being  shorter  than  the  remaining  three,  next  left  the  ground, 
and  gradually  disappeared.  [Fig.  81  B.]  Of  the  three  remaining 
toes,  the  middle  or  axial  one  was  the  longest,  and  retaining  its 
supremacy  as  greater  strength  and  speed  were  required,  finally 
assumed  the  chief  support  of  the  foot  [Fig.  81  C],  while  the 
outer  digits  left  the  ground,  ceased  to  be  of  use,  and  were  lost, 
except  as  splint-bones  [Fig.  81  D].  The  feet  of  the  existing 
horse  shows  the  best  example  of  this  reduction  in  the  Peris- 
sodactyls,  as  it  is  the  most  specialized  known  in  the  Ungulates 
[Fig.  81  D]. 

In  the  artiodactyl  foot,  the  reduction  resulted  in  the  gradual 
diminution  of  the  two  outer  of  the  four  remaining  toes,  the  third 
and  fourth  doing  all  the  work,  and  thus  increasing  in  size  and 
power.  The  fifth  digit,  for  the  same  reasons  as  in  the  perisso- 
dactyl foot,  first  left  the  ground  and  became  smaller.  Next,  the 
second  soon  followed,  and  these  two  gradually  ceased  to  be 
functional,  [and  eventually  disappeared  altogether,  as  shown  in 
the  accompanying  drawing  of  the  feet  of  still  existing  animals, 
Fig.  82  B,  C,  D]. 

The  limb  of  the  modern  race-horse  is  a  nearly  perfect  piece  of 
machinery,  especially  adapted  to  great  speed  on  dry,  level 
ground.  The  limb  of  an  antelope,  or  deer,  is  likewise  well  fitted 


P a  l&  on  to  logy. 

b  C  d 


Equus :  Qua- 
ternary and 
Recent. 


Pliohippus : 
Pliocene. 


Orohippus  : 
Eocene. 


FIG.  83.— Feet  and  teeth  in  fossil  pedigree  of  the  Horse.  (After  Marsh.) 
a,  bones  of  the  fore-foot ;  b,  bones  of  the  hind-foot ;  c,  radius  and  ulna ; 
d,  tibia  and  fibula ;  e,  roots  of  a  tooth ;  f  and  g,  crowns  of  upper  and 
lower  molar  teeth. 


igo          Darwin,  and  after  Larwtn. 

for  rapid  motion  on  a  plain,  but  the  foot  itself  is  adapted  to  rough 
mountain  work  as  well,  and  it  is  to  this  advantage,  in  part,  that 
the  Artiodactyls  owe  their  present  supremacy.  The  plantigrade 
pentadactyl  foot  of  the  primitive  Ungulate — and  even  the  peris- 
sodactyl  foot  that  succeeded  it— both  belong  to  the  past  humid 
period  of  the  world's  history.  As  the  surface  of  the  earth 
slowly  dried  up,  in  the  gradual  desiccation  still  in  progress,  new 
types  of  feet  became  a  necessity,  and  the  horse,  antelope, 
and  camel  were  gradually  developed,  to  meet  the  altered 
conditions. 


FIG.  %±—Pala:otherium.     (Lower  Tertiary  of  Paris  Basin.) 

The  best  instance  of  such  progressive  modifications 
in  the  case  of  perissodactyl  feet  is  furnished  by  the 
fossil  pedigree  of  the  existing  horse,  because  here, 
within  the  limits  of  the  same  continuous  family  line, 
we  have  presented  the  entire  series  of  modifications. 

There  are  now  known  over  thirty  species  of  horse- 
like  creatures,  beginning  from  the  size  of  a  fox,  then 
progressively  increasing  in  bulk,  and  all  standing  in 


Palceontology.  \  9 1 

linear  series  in  structure  as  in  time.  Confining 
attention  to  the  teeth  and  feet,  it  will  be  seen  from 
the  wood-cut  on  page  189  that  the  former  grow 
progressively  longer  in  their  sockets,  and  also  more 
complex  in  the  patterns  of  their  crowns.  On  the 
other  hand,  the  latter  exhibit  a  gradual  diminution 
of  their  lateral  toes,  together  with  a  gradual  strength- 
ening of  the  middle  one.  (See  Fig.  83.)  So  that  in 
the  particular  case  of  the  horse-ancestry  we  have  a 
practically  complete  chain  of  what  only  a  few  years 
ago  were  "  missing  links."  And  this  now  practically 
completed  chain  shows  us  the  entire  history  of  what 
happens  to  be  the  most  peculiar,  or  highly  specialized, 
limb  in  the  whole  mammalian  class — namely,  that  of 
the  existing  horse.  Of  the  other  two  wood-cuts,  the 
former  (Fig.  84)  shows  the  skeleton  of  a  very  early 
and  highly  generalized  ancestor,  while  the  other  is 
a  partial  restoration  of  a  much  more  recent  and 
specialized  one.  (Fig.  85.) 

On  the  other  hand,  progressive  modifications  of  the 
artiodactyl  feet  may  be  traced  geologically  up  to  the 
different  stages  presented  by  living  ruminants,  in  some 
of  which  it  has  proceeded  further  than  in  others.  For 
instance,  if  we  compare  the  pig,  the  deer,  and  the 
camel  (Fig.  82),  we  immediately  perceive  that  the 
dwindling  of  the  two  rudimentary  digits  has  pro- 
ceeded much  further  in  the  case  of  the  deer  than  in 
that  of  the  pig,  and  yet  not  so  far  as  in  that 
of  the  camel,  seeing  that  here  they  have  wholly 
disappeared.  Moreover,  complementary  differences 
are  to  be  observed  in  the  degree  of  consolidation 
presented  by  the  two  useful  digits.  For  while  in  the 
pig  the  two  foot-bones  are  still  clearly  distinguish- 


192          Darwin,  and  after  Darwin. 

able  throughout  their  entire  length,  in  the  deer,  and 
still  more  in  the  camel,  their  union  is  more  complete, 
so  that  they  go  to  constitute  a  single  bone,  whose 
double  or  compound  character  is  indicated  externally 
only  by  a  slight  bifurcation  at  the  base.  Nevertheless, 
if  we  examine  the  state  of  matters  in  the  unborn 
young  of  these  animals,  we  find  that  the  two  bones 
in  question  are  still  separated  throughout  their  length, 


FIG.  ^.—Hipparion.     (New  World  Pliocene.) 

and  thus  precisely  resemble  what  used  to  be  their 
permanent  condition  in  some  of  the  now  fossil  species 
of  hoofed  mammalia. 

Turning  next  from  bones  of  the  limb  to  other  parts 
of  the  mammalian  skeleton,  let  us  briefly  consider  the 
evidence  of  evolution  that  is  here  likewise  presented  by 
the  vertebral  column,  the  skull,  and  the  teeth. 

As  regards  the  vertebral  column,  if  we  examine  this 


Paleontology.  193 

structure  in  any  of  the  existing  hoofed  animals,  we 
find  that  the  bony  processes  called  zygapophyses, 
which  belong  to  each  of  the  constituent  vertebrae, 
are  so  arranged  that  the  anterior  pair  belonging  to 
each  vertebra  interlocks  with  the  posterior  pair  be- 
longing to  the  next  vertebra.  In  this  way  the  whole 
series  of  vertebrae  are  connected  together  in  the  form 
of  a  chain,  which,  while  admitting  of  considerable 
movement  laterally,  is  everywhere  guarded  against 
dislocation.  But  if  we  examine  the  skeletons  of  any 
ungulates  from  the  lower  Eocene  deposits,  we  find 
that  in  no  case  is  there  any  such  arrangement  to 
secure  interlocking.  In  all  the  hoofed  mammals  of 
this  period  the  zygapophyses  are  flat.  Now,  from 
this  flat  condition  to  the  present  condition  of  full 
interlocking  we  obtain  a  complete  series  of  connecting 
links.  In  the  middle  Miocene  period  we  find  a  group 
of  hoofed  animals  in  which  the  articulation  begins 
by  a  slight  rounding  of  the  previously  flat  surfaces: 
later  on  this  rounding  progressively  increases,  until 
eventually  we  get  the  complete  interlocking  of  the 
present  time. 

As  regards  teeth,  and  still  confining  attention  to 
the  hoofed  mammals,  we  find  that  low  down  in  the 
geological  series  the  teeth  present  on  their  grinding 
surfaces  only  three  simple  tubercles.  Later  on  a 
fourth  tubercle  is  added,  and  later  still  there  is  de- 
veloped that  complicated  system  of  ridges  and  furrows 
which  is  characteristic  of  these  teeth  at  the  present 
time,  and  which  was  produced  by  manifold  and 
various  involutions  of  the  three  or  four  simple  tuber- 
cles of  Eocene  and  lower  Miocene  times.  In  other 
words,  the  principle  of  gradual  improvement  in  the 

*  O 


194  Darwin,  and  after  Darwin. 

A  B 


.  these  two  parts  ot  the  Drain  nave  grown  to  so 
he  other  parts  from  the  superficial  points  of  view 


Palceontology.  j^c 

construction  of  teeth,  which  has  already  been  depicted 
as  regards  the  particular  case  of  the  Horse-family  (Fig. 
83),  is  no  less  apparent  in  the  pedigree  of  all  the 
other  mammalia,  wherever  the  palsontological  history 
is  sufficiently  intact  to  serve  as  a  record  at  all. 


FIG.  87.— Ideal  section  through  all  the  above  stages.   (After  Le  Conte.) 

Lastly,  as  regards  the  skull,  casts  of  the  interior 
show  that  all  the  earlier  mammals  had  small  brains 
with  comparatively  smooth  or  unconvoluted  surfaces  ; 
and  that  as  time  went  on  the  mammalian  brain 
gradually  advanced  in  size  and  complexity.  Indeed 
so  small  were  the  cerebral  hemispheres  of  the  primitive 
mammals  that  they  did  not  overlap  the  cerebellum, 
while  their  smoothness  must  have  been  such  as  in  this 
respect  to  have  resembled  the  brain  of  a  bird  or  reptile. 
This,  of  course,  is  just  as  it  ought  to  be,  if  the  brain, 
which  the  skull  has  to  accommodate,  has  been  gradually 
O  2 


196          Darwin,  and  after  Darwin. 

evolved  into  larger  and  larger  proportions  in  respect  of 
its  cerebral  hemispheres,  or  the  upper  masses  of  it 
which  constitute  the  seat  of  intelligence.  Thus,  if  we 
look  at  the  above  series  of  wood-cuts,  which  re- 
presents the  comparative  structure  of  the  brain  in  the 
existing  classes  of  the  Vertebrata,  we  can  immediately 
understand  why  the  fossil  skulls  of  Mammalia  should 
present  a  gradual  increase  in  size  and  furrowing,  so 
as  to  accommodate  the  general  increase  of  the  brain 
in  both  these  respects  between  the  level  marked 
"  maml  "  and  that  marked  "  man,"  in  the  last  of  the 
diagrams.  (Fig.  87.) 

The  tabular  statement  on  the  following  diagram, 
which  I  borrow  from  Prof.  Cope,  will  serve  at  a  glance 
to  reveal  the  combined  significance  of  so  many  lines 
of  evidence,  united  within  the  limits  of  the  same  group 
of  animals. 

To  give  only  one  special  illustration  of  the  principle 
of  evolution  as  regards  the  skull,  here  is  one  of  the 
most  recent  instances  that  has  occurred  of  the  dis- 
covery of  a  missing  link,  or  connecting  form  (see 
Fig.  88).  The  fossil  (B),  which  was  found  in  New 
Jersey,  stands  in  an  intermediate  position  between  the 
stag  and  the  elk.  In  the  stag  (A)  the  skull  is  high, 
showing  but  little  of  that  anterior  attenuation  which 
is  such  a  distinctive  feature  of  the  skull  of  the  elk  (C). 
The  nasal  bones  (N)  of  the  former,  again,  are  re- 
markably long  when  compared  with  the  similar  bones 
of  the  latter,  and  the  premaxillaries  (PMX),  instead 
of  being  projected  forward  along  the  horizontal  plane 
of  the  base  of  the  skull,  are  deflected  sharply  down- 
ward. In  all  these  points,  it  will  be  seen,  the  newly 
discovered  form  (Cervalces)  holds  an  intermediate 


Pal&ontology. 


197 


V        ~          V 

m  M  k 


§10 If    III II 

K  2 


II 


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and  ce 


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198  Darwin,  and  after  Darwin. 

position  (B).     "  The  skull  exhibits  a  partial  attenua- 
tion anteriorly,  the  premaxillaries  are  directed  about 


FIG.  88.— Skulls  of— A,  Canadian  Stag ;  B,  Cervakes  American™ ; 
and  C,  Elk.     (After  Heilprin.) 

equally  downward  and  forward,  and  the  nasal  bones 
are  measurably  contracted  in  size.     The  horns  like- 


Paleontology,  1 99 

wise  furnish  characters  which  further  serve  to  establish 
this  dual  relationship1." 

The  evidence,  then,  which  is  furnished  by  all  parts 
of  the  vertebral  skeleton — whether  we  have  regard  to 
Fishes,  Reptiles,  Birds,  or  Mammals — is  cumulative 
and  consistent.  Nowhere  do  we  meet  with  any  de- 
viation or  ambiguity,  while  everywhere  we  encounter 
similar  proofs  of  continuous  transformation — proofs 
which  vary  only  with  the  varying  amount  of  material 
which  happens  to  be  at  our  disposal,  being  most 
numerous  and  detailed  in  those  cases  where  the 
greatest  number  of  fossil  forms  has  been  preserved 
by  the  geological  record.  Here,  therefore,  we  may 
leave  the  vertebral  skeleton ;  and,  having  presented 
a  sample  of  the  evidence  as  yielded  by  horns  and 
bones,  I  will  conclude  by  glancing  with  similar  brevity 
at  the  case  of  shells — which,  as  before  remarked,  con- 
stitute the  only  other  sufficiently  hard  or  permanent 
material  to  yield  unbroken  evidence  touching  the 
fossil  ancestry  of  animals. 

Of  course  it  will  be  understood  that  I  am  everywhere 
giving  merely  samples  of  the  now  superabundant 
evidence  which  is  yielded  by  palaeontology  ;  and,  as 
this  chapter  is  already  a  long  one,  I  must  content 
myself  with  citing  only  the  case  of  mollusk-shells, 
although  shells  of  other  classes  might  be  made  to 
yield  highly  important  additions  to  the  testimony. 
Moreover,  even  as  regards  the  one  division  of  mollusk-- 
shells, I  can  afford  to  quote  only  a  very  few  cases. 
These,  however,  are  in  my  opinion  the  strongest 
single  pieces  of  evidence  in  favour  of  transmutation 
which  have  thus  far  been  brought  to  light. 

1  Heilprin,  Geological  Evidences  of  Evolution,  pp.  73-4  (1888). 


2OO          Darwin,  and  after  Darwin. 

Near  the   village  of  Steinheim,  in  Wiirtember^, 
there  is  an  ancient  lake-basin,  dating  from  Tertiary 


in  ii  i 

FlG.  89.— Transmutations  of  Planorbis.     (After  Hyatt.) 

times.  The  lake  has  long  ago  dried  up ;  but  its 
aqueous  deposits  are  extraordinarily  rich  in  fossil 
shells,  especially  of  different  species  of  the  genus 


Paleontology.  201 

Planorbis.     The  following  is  an  authoritative  resumt 
of  the  facts. 

As  the  deposits  seem  to  have  been  continuous  for  ages,  and 
the  fossil  shells  very  abundant,  this  seemed  to  be  an  excellent 
opportunity  to  test  the  theory  of  derivation.  With  this  end  in 
view,  they  have  been  made  the  subject  of  exhaustive  study  by 
Hilgendorf  in  1866,  and  by  Hyatt  in  1880.  In  passing  from  the 
lowest  to  the  highest  strata  the  species  change  greatly  and  many 
times,  the  extreme  forms  being  so  different  that,  were  it  not  for 
the  intermediate  forms,  they  would  be  called  not  only  different 
species,  but  different  genera.  And  yet  the  gradations  are  so  in- 
sensible that  the  whole  series  is  nothing  less  than  a  demon- 
stration, in  this  case  at  least,  of  origin  of  species  by  derivation 
with  modifications.  The  accompanying  plate  of  successive  forms 
(Fig.  89),  which  we  take  from  Prof.  Hyatt's  admirable  memoir, 
will  show  this  better  than  any  mere  verbal  explanation.  It  will 
be  observed  that,  commencing  with  four  slight  varieties— pro- 
bably sexually  isolated  varieties— of  one  species,  each  series 
shows  a  gradual  transformation  as  we  go  upward  in  the  strata — 
i.e.  onward  in  time.  Series  I  branches  into  three  sub-series,  in 
two  of  which  the  change  of  form  is  extreme.  Series  IV  is  re- 
markable for  great  increase  in  size  as  well  as  change  in  form. 
In  the  plate  we  give  only  selected  stages,  but  in  the  fuller  plates 
of  the  memoir,  and  still  more  in  the  shells  themselves,  the  sub- 
tilest  gradations  are  found 1. 

Here  is  another  and  more  recently  observed  case  of 
transmutation  in  the  case  of  mollusks. 

The  recent  species,  Strombus  accipitrinus,  still  in- 
habits the  coasts  of  Florida.  Its  extinct  prototype, 
J>.  Leidy,  was  discovered  a  few  years  ago  by  Prof. 
Heilprin  in  the  Pliocene  formations  of  the  interior 
of  Florida.  The  peculiar  shape  of  the  wing,  and 
tuberculation  of  the  whorl,  are  thus  proved  to  have 
grown  out  of  a  previously  more  conical  form  of 
shell. 

1  Le  Conte,  loc.  cit.,  pp.  236-7. 


Paleontology.  203 

Lastly,  attention  may  here  again  be  directed  to  the 
very  instructive  series  of  shells  which  has  already 
been  shown  in  a  previous  chapter,  and  which  serves 
to  illustrate  the  successive  geological  forms  ofPaludina 
from  the  Tertiary  beds  of  Slavonia,  as  depicted  by 
Prof.  Neumayr  of  Vienna.  (Fig.  i,  p.  19.) 


CHAPTER  VI. 

GEOGRAPHICAL  DISTRIBUTION. 

THE  argument  from  geology  is  the  argument  from 
the  distribution  of  species  in  time.  I  will  next  take 
the  argument  from  the  distribution  of  species  in  space — 
that  is,  the  present  geographical  distribution  of  plants 
and  animals. 

Seeing  that  the  theory  of  descent  with  adaptive 
modification  implies  slow  and  gradual  change  of  one 
species  into  another,  and  progressively  still  more  slow 
and  gradual  changes  of  one  genus,  family,  or  order 
into  another  genus,  family,  or  order,  we  should  expect 
on  this  theory  that  the  organic  types  living  on  any 
given  geographical  area  would  be  found  to  resemble 
or  to  differ  from  organic  types  living  elsewhere,  ac- 
cording as  the  area  is  connected  with  or  disconnected 
from  other  geographical  areas.  For  instance,  the 
large  continental  islands  of  Australia  and  New  Zealand 
are  widely  disconnected  from  all  other  lands  of  the 
world,  and  deep  sea  soundings  show  that  they  have 
probably  been  thus  disconnected,  either  since  the  time 
of  their  origin,  or,  at  the  least,  through  immense 
geological  epochs.  The  theory  of  evolution,  there- 
fore, would  expect  to  find  two  general  facts  with 
regard  to  the  inhabitants  of  these  islands.  First,  that 


Geographical  Distribution.  205 

the  inhabitants  should  form,  as  it  were,  little  worlds  of 
their  own,  more  or  less  unlike  the  inhabitants  of  any 
other  parts  of  the  globe.  And  next,  that  some  of 
these  inhabitants  should  present  us  with  independent 
information  touching  archaic  forms  of  life.  For  it  is 
manifestly  most  improbable  that  the  course  of  evo- 
lutionary history  should  have  run  exactly  parallel  in 
the  case  of  these  isolated  oceanic  continents  and  in 
continents  elsewhere.  Australia  and  New  Zealand, 
therefore,  ought  to  present  a  very  large  number,  not 
only  of  peculiar  species  and  genera,  but  even  of 
families,  and  possibly  of  orders.  Now  this  is  just 
what  Australia  and  New  Zealand  do  present.  The 
case  of  the  dog  being  doubtful,  there  is  an  absence  of 
all  mammalian  life,  except  that  of  one  of  the  oldest 
and  least  highly  developed  orders,  the  Marsupials. 
There  even  occurs  a  unique  order,  still  lower  in  the 
scale  of  organization — so  low,  in  fact,  that  it  deserves 
to  be  regarded  as  but  nascent  mammalian :  I  mean, 
of  course,  the  Monotremata.  As  regards  Birds,  we 
have  the  peculiar  wingless  forms  alluded  to  in  a 
previous  chapter  (viz.  that  on  Morphology) ;  and,  with- 
out waiting  to  go  into  details,  it  is  notorious  that  the 
faunas  of  Australia  and  New  Zealand  are  not  only 
highly  peculiar,  but  also  suggestively  archaic.  Therefore, 
in  both  the  respects  above  mentioned,  the  anticipations 
of  our  theory  are  fully  borne  out.  But  as  it  would 
take  too  long  to  consider,  even  cursorily,  the  faunas 
and  floras  of  these  immense  islands,  I  here  allude  to 
them  only  for  the  sake  of  illustration.  In  order  to 
present  the  argument  from  geographical  distribution 
within  reasonable  limits,  I  think  it  is  best  to  restrict 
our  examination  to  smaller  areas  ;  for  these  will  better 


206          Darwin,  and  after  Darwin. 

admit  of  brief  and  yet  adequate  consideration.  But 
of  course  it  will  be  understood  that  the  less  isolated 
the  region,  and  the  shorter  the  time  that  it  has  been 
isolated,  the  smaller  amount  of  peculiarity  should  we 
expect  to  meet  with  on  the  part  of  its  present  in- 
habitants. Or,  conversely  stated;  the  longer  and  the 
greater  the  isolation,  the  more  peculiarity  of  species 
would  our  theory  expect  to  find.  The  object  of  the 
present  chapter  will  be  to  show  that  these,  and  other 
cognate  expectations,  are  fully  realized  by  facts  ;  but, 
before  proceeding  to  do  this,  I  must  say  a  few  words 
on  the  antecedent  standing  of  the  argument. 

Where  the  question  is,  as  at  present,  between  the 
rival  theories  of  special  creation  and  gradual  trans- 
mutation, it  may  at  first  sbht  well  appear  that  no  test 
can  be  at  once  so  crucial  and  so  easily  applied  as  this 
of  comparing  the  species  of  one  geographical  area 
with  those  of  another,  in  order  to  see  whether 
there  is  any  constant  correlation  between  differences 
of  type  and  degrees  of  separation.  But  a  little  further 
thought  is  enough  to  show  that  the  test  is  not  quite  so 
simple  or  so  absolute — that  it  is  a  test  to  be  applied 
in  a  large  and  general  way  over  the  surface  of  the 
whole  earth,  rather  than  one  to  be  relied  upon  as 
exclusively  rigid  in  every  special  case. 

In  the  first  place,  there  is  the  obvious  consideration 
that  lands  or  seas  which  are  discontinuous  now  may 
not  always  have  been  so,  or  not  for  long  enough  to 
admit  of  the  effects  of  separation  having  been  exerted 
to  any  considerable  extent  upon  their  inhabitants. 
Next,  there  is  the  scarcely  less  important  consideration, 
that  although  land  areas  may  long  have  been  sepa- 
rated from  one  another  by  extensive  tracts  of  ocean, 


Geographical  Distribution.  207 

birds  and  insects  may  more  or  less  easily  have  been 
able  to  fly  from  one  to  the  other;  while  even  non- 
flyirg  animals  and  plants  may  often  have  been 
transported  by  floating  ice  or  timber,  wind  or  water 
currents,  and  sundry  other  means  of  dispersal.  Again, 
there  is  the  important  influence  of  climate  to  be  taken 
into  account.  We  know  from  geological  evidence  that 
in  the  course  of  geological  time  the  self-same  con- 
tinents have  been  submitted  to  enormous  changes  of 
temperature — varying  in  fact  from  polar  cold  to  almost 
tropical  heat ;  and  as  it  is  manifestly  impossible  that 
forms  of  life  suited  to  one  of  these  climates  could 
have  survived  during  the  other,  we  can  here  perceive  a 
further  and  most  potent  cause  interfering  with  the  test 
of  geographical  distribution  as  indiscriminately  applied 
in  all  cases.  When  the  elephant  and  hippopotamus 
were  flourishing  in  England  amid  the  luxuriant  vege- 
tation which  these  large  animals  require,  it  is  evident 
that  scarcely  any  one  species  of  either  the  fauna  or 
the  flora  of  this  country  can  have  been  the  same  as  it 
was  when  its  African  climate  gave  place  to  that  of 
Greenland.  Therefore,  as  Mr.  Wallace  observes,  "  If 
glacial  epochs  in  temperate  lands  and  mild  climates 
near  the  poles  have,  as  now  believed  by  men  of 
eminence,  occurred  several  times  over  in  the  past 
history  of  the  earth,  the  effects  of  such  great  and 
repeated  changes  both  on  migration,  modification,  and 
extinction  of  species,  must  have  been  of  overwhelming 
importance — of  more  importance  perhaps  than  even 
the  geological  changes  of  sea  and  land/' 

But  although  for  these,  and  certain  other  less 
important  reasons  which  I  need  not  wait  to  detail,  we 
must  conclude  that  the  evidence  from  geographical 


208  Darwin^  and  after  Darwin. 

distribution  is  not  to  be  regarded  as  a  crucial  test 
between  the  rival  theories  of  creation  and  evolution 
in  all  cases  indiscriminately,  I  must  next  remark  that 
it  is  undoubtedly  one  of  the  strongest  lines  of  evidence 
which  we  possess.  When  we  once  remember  that, 
according  to  the  general  theory  of  evolution  itself,  the 
present  geographical  distribution  of  plants  and  animals 
is  "the  visible  outcome  or  residual  product  of  the 
whole  past  history  of  the  earth,"  and,  therefore,  that  of 
the  conditions  determining  the  characters  of  life  in- 
habiting this  and  that  particular  area  continuity  or 
discontinuity  with  other  areas  is  but  one, — when  we 
remember  this,  we  find  that  no  further  reservation  has 
to  be  made:  all  the  facts  of  geographical  distribution 
speak  with  one  consent  in  favour  of  the  naturalistic 
theory. 

The  first  of  these  facts  which  I  shall  adduce  is,  that 
although  the  geographical  range  of  any  given  species 
is,  as  a  rule,  continuous,  such  is  far  from  being 
always  the  case.  Very  many  species  have  more  or 
less  discontinuous  ranges — the  mountain-hare,  for 
instance,  extending  from  the  Arctic  regions  over  the 
greater  portion  of  Europe  to  the  Ural  Mountains  and 
the  Caucasus,  and  yet  over  all  this  enormous  tract 
appearing  only  in  isolated  or  discontinuous  patches, 
where  there  happen  to  be  either  mountain  ranges  or 
climates  cold  enough  to  suit  its  nature.  Now,  in  all 
such  cases  of  discontinuity  in  the  range  of  a  species 
the  theory  of  evolution  has  a  simple  explanation  to 
offer — namely,  either  that  some  representatives  of  the 
species  have  at  some  former  period  been  able  to 
migrate  from  one  region  to  the  other,  or  else  that  at 


Geographical  Distribution.  209 

one  time  the  species  occupied  the  whole  of  the  range 
in  question,  but  afterwards  became  broken  up  as 
geographical,  climatic,  or  other  changes  rendered 
parts  of  the  area  unfit  for  the  species  to  inhabit. 
Thus,  for  instance,  it  is  easy  to  understand  that 
during  the  last  cold  epoch  the  mountain-hare  would 
have  had  a  continuous  range ;  but  that  as  the  Arctic 
climate  gradually  receded  to  polar  regions,  the  species 
would  be  able  to  survive  in  southern  latitudes  only 
on  mountain  ranges,  and  thus  would  become  broken 
up  into  many  discontinuous  patches,  corresponding 
with  these  ranges.  In  the  same  way  we  can  explain 
the  occurrence  of  Arctic  vegetation  on  the  Alps  and 
Pyrenees — namely,  as  left  behind  by  the  retreat  of 
the  Arctic  climate  ;it  the  close  of  the  glacial  period. 

But  now,  on  the  other  hand,  the  theory  of  special 
creation  cannot  so  well  afford  to  render  this  obvious 
explanation  of  discontinuity.  In  the  case  of  the 
Arctic  flora  of  the  Alps,  for  instance,  although  it  is 
true  that  much  of  this  vegetation  is  of  an  Arctic  type, 
it  is  not  true  that  the  species  are  all  identical  with 
those  which  occur  in  the  Arctic  regions.  Therefore 
the  theory  of  special  creation  would  here  have  to 
assume  that,  although  the  now  common  species  were 
left  behind  on  the  Alps  by  the  retreat  of  glaciation 
northwards,  the  peculiar  Alpine  species  were  after- 
wards created  separately  upon  the  Alps,  and  yet 
created  with  such  close  affinities  to  the  pre-existing 
species  as  to  be  included  with  them  under  the  same 
genera.  Looking  to  the  absurdity  of  this  supposition, 
as  well  as  of  others  which  I  need  not  wait  to  mention, 
certain  advocates  of  special  creation  have  sought  to 
take  refuge  in  another  hypothesis — namely,  that 

*  P 


2io  Darwin,  and  after  Darwin. 

species  which  present  a  markedly  discontinuous  range 
may  have  had  a  corresponding  number  of  different 
centres  of  creation,  the  same  specific  type  having 
been  turned  down,  so  to  speak,  on  widely  separated 
areas.  But  to  me  it  seems  that  this  explanation  pre- 
sents even  greater  difficulty  than  the  other.  If  it  is 
difficult  to  say  why  the  Divinity  should  have  chosen 
to  create  new  species  of  plants  on  the  Alps  on  so 
precisely  the  same  pattern  as  the  old,  much  more 
would  it  be  difficult  to  say  why,  in  addition  to  these 
new  species,  he  should  also  have  created  again  the 
old  species  which  he  had  already  placed  in  the  Arctic 
regions. 

So  much,  then,  for  discontinuity  of  distribution. 
The  next  general  fact  to  be  adduced  is,  that  there 
is  no  constant  correlation  between  habitats  and  ani- 
mals or  plants  suited  to  live  upon  them.  Of  course 
all  the  animals  and  plants  living  upon  any  given  area 
are  well  suited  to  live  upon  that  area  ;  for  otherwise 
they  could  not  be  there.  But  the  point  now  is,  that 
besides  the  area  on  which  they  do  live,  there  are 
usually  many  other  areas  in  different  parts  of  the 
globe  where  they  might  have  lived  equally  well — as 
is  proved  by  the  fact  that  when  transported  by  man 
they  thrive  as  well,  or  even  better,  than  in  their 
native  country.  Therefore,  upon  the  supposition  that 
all  species  were  separately  created  in  the  countries 
where  they  are  respectively  found,  we  must  conclude 
that  they  were  created  in  only  some  of  the  places 
where  they  might  equally  well  have  lived.  Probably 
there  is  at  most  but  a  small  percentage  either  of 
plants  or  animals  which  would  not  thrive  in  some 


Geographical  Distribution.  211 

place,  or  places,  on  the  earth's  surface  other  than 
that  in  which  they  occur ;  and  hence  we  must  say 
that  one  of  the  objects  of  special  creation— if  this 
be  the  true  theory — was  that  of  depositing  species 
in  only  some  among  the  several  parts  of  the  earth's 
surface  equally  well  suited  to  support  them. 

Now,  I  do  not  contend  that  this  fact  in  itself  raises 
any  difficulty  against  the  theory  of  special  creation. 
But  I  do  think  that  a  very  serious  difficulty  is  raised 
when  to  this  fact  we  add  another — namely,  that  on 
every  biological  region  we  encounter  species  related 
to  other  species  in  genera,  and  usually  also  genera 
related  to  other  genera  in  families.  For  if  each  of 
all  the  constituent  species  of  a  genus,  and  even  of  a 
family,  were  separately  created,  we  must  hence  con- 
clude that  in  depositing  them  there  was  an  unaccount- 
able design  manifested  to  make  areas  of  distribution 
correspond  to  the  natural  affinities  of  their  inhabi- 
tants. For  example,  the  humming-birds  are  geogra- 
phically restricted  to  America,  and  number  120 
genera,  comprising  over  400  species.  Hence,  if  this 
betokens  400  separate  acts  of  creation,  it  cannot 
possibly  have  been  due  to  chance  that  they  were 
all  performed  on  the  same  continent  :  it  must  have 
been  design  which  led  to  every  species  of  this  large 
family  of  birds  having  been  deposited  in  one  geogra- 
phical area.  Or,  to  take  a  case  where  only  the 
species  of  a  single  genus  are  concerned.  The  rats 
and  mice  proper  constitute  a  genus  which  comprises 
altogether  more  than  100  species,  and  they  are  all 
exclusively  restricted  to  the  Old  World.  In  the 
New  World  they  are  represented  by  another  genus 
comprising  about  70  species,  which  resemble  their 
P  2 


212  Darwin,  and  after  Darwin. 

Old  World  cousins  in  form  and  habits  ;  but  differ 
from  them  in  dentition  and  other  such  minor  points. 
Now,  the  question  is, — Why  should  all  the  100 
species  have  been  separately  created  on  one  side 
of  the  Atlantic  with  one  pattern  of  dentition,  and 
all  the  70  species  on  the  other  side  with  another 
pattern?  What  has  the  Atlantic  Ocean  got  to  do 
with  any  "  archetypal  plan  "  of  rats'  teeth  ? 

Or  again,  to  recur  to  Australia,  why  should  all 
the  mammalian  forms  of  life  be  restricted  to  the 
one  group  of  Marsupials,  when  we  know  that  not 
only  the  Rodents,  such  as  the  rabbit,  but  all  other 
orders  of  mammals,  would  thrive  there  equally  well. 
And  similarly,  of  course,  in  countless  other  instances. 
Everywhere  we  meet  with  this  same  correlation 
between  areas  of  distribution  and  affinities  of  classifi- 
cation. 

Now,  it  is  at  once  manifest  how  completely  this 
general  fact  harmonizes  with  the  theory  of  evolution. 
If  the  400  species  of  humming-birds,  for  instance,  are  all 
modified  descendants  of  common  ancestors,  and  if  none 
of  their  constituent  individuals  have  ever  been  large 
enough  to  make  their  way  across  the  oceans  which 
practically  isolate  their  territory  from  all  other  tropi- 
cal and  sub-tropical  regions  of  the  globe,  then  we  can 
understand  why  it  is  that  all  the  400  species  occupy 
the  same  continent.  But  on  the  special-creation 
theory  we  can  see  no  reason  why  the  400  species 
should  all  have  been  deposited  in  America.  And,  as 
already  observed,  we  must  remember  that  this  corre- 
lation between  a  geographically  restricted  habitat 
and  the  zoological  or  botanical  affinities  of  its  inhabi- 
tants, is  repeated  over  and  over  and  over  again  in  the 


Geographical  Distribution.  213 

faunas  and  floras  of  the  world,  so  that  merely  to 
enumerate  the  instances  would  require  a  separate 
chapter. 

Furthermore,  the  general  argument  thus  presented 
in  favour  of  descent  with  continuous  modification 
admits  of  being  enormously  strengthened  by  three 
different  classes  of  additional  facts. 

The  first  is,  that  the  correlation  in  question — 
namely,  that  between  a  geographically  restricted 
habitat  and  the  zoological  or  botanical  affinities  of 
its  inhabitants — is  not  limited  to  the  now  existing 
species,  but  extends  also  to  the  extinct.  That  is  to 
say,  the  dead  species  are  allied  to  the  living  species, 
as  we  should  expect  that  they  must  be.  if  the  latter 
are  modified  descendants  of  the  former.  On  the 
alternative  theory,  however,  we  have  to  suppose  that 
the  policy  of  maintaining  a  correlation  between  geo- 
graphical restriction  and  natural  affinity  extends  very- 
much  further  back  than  even  the  existing  species 
of  plants  and  animals ;  indeed  we  must  suppose  that 
a  practically  infinite  number  of  additional  acts  of 
separate  creation  were  governed  by  the  same  policy, 
in  the  case  of  long  lines  of  species  long  since  extinct. 

Thus  far,  then,  the  only  answer  which  an  advocate 
of  special  creation  can  adduce  is,  that  for  some  reason 
unknown  to  us  such  a  policy  may  have  been  more  wise 
than  it  appears  :  it  may  have  served  some  inscrutable 
purpose  that  allied  products  of  distinct  acts  of  crea- 
tion should  all  be  kept  together  on  the  same  areas. 
Well,  in  answer  to  this  unjustifiable  appeal  to  the 
argument  from  ignorance,  I  will  adduce  the  second 
of  the  three  considerations.  This  is,  that  in  cases 
where  the  geographical  areas  are  not  restricted  the 


214  Darwin,  and  after  Darwin. 

policy  in  question  fails.  In  other  words,  where  the 
inhabitants  of  an  area  are  free  to  migrate  to  other 
areas,  the  policy  of  correlating  affinity  with  distribu- 
tion is  most  significantly  forgotten.  In  this  case 
species  wander  away  from  their  native  homes,  and 
the  course  of  their  wanderings  is  marked  by  the 
origination  of  new  species  springing  up  en  route. 
Now,  is  it  reasonable  to  suppose  that  the  mere  cir- 
cumstance of  some  members  of  a  species  being  able 
to  leave  their  native  home  should  furnish  any  occasion 
for  creating  new  and  allied  species  upon  the  tracts  over 
which  they  travel,  or  the  territories  to  which  they  go? 
When  the  400  existing  species  of  humming-birds 
have  all  been  created  on  the  same  continent  for  some 
reason  supposed  to  be  unknown,  why  should  this 
reason  give  way  before  the  accident  of  any  means 
of  migration  being  furnished  to  humming-birds,  so 
that  they  should  be  able  to  visit,  say  the  continents 
of  Africa  and  Asia,  there  gain  a  footing  beside  the 
sun-birds,  and  henceforth  determine  a  new  centre  for 
the  separate  creation  of  additional  species  of  hum- 
ming-birds peculiar  to  the  Old  World — as  has  hap- 
pened in  the  case  of  the  majority  of  species  which, 
unlike  the  humming-birds,  have  been  at  any  time 
free  to  migrate  from  their  original  homes  ? 

Lastly,  my  third  consideration  is,  that  the  supposed 
policy  in  question  does  not  extend  to  affinities  which 
are  wider  than  those  between  species  and  genera — 
more  rarely  to  families,  scarcely  ever  to  orders,  and 
never  to  classes.  In  other  words,  nature  shows  a 
double  correlation  in  her  geographical  distribution 
of  organic  types : — first,  that  which  we  have  already 
considered  between  geographical  restriction  and 


Geographical  Distribution.  215 

natural  affinity  among  inhabitants  of  the  same  areas  ; 
second,  another  of  a  more  detailed  character  between 
degrees  of  geographical  restriction  and  degrees  of 
natural  affinity.  The  more  distant  the  affinity,  the 
more  general  is  the  extension.  This,  of  course,  is 
what  we  should  expect  on  the  theory  of  descent 
with  modification,  because  the  more  distant  the 
affinity,  and  therefore,  ex  kypothesi,  the  larger  and 
the  older  the  original  group  of  organisms,  the  greater 
must  be  the  chance  of  dispersal.  The  400  species 
of  humming-birds  may  well  be  unable  to  migrate 
from  their  native  continent ;  but  it  would  indeed 
have  been  an  unaccountable  fact  if  no  other  species 
of  all  the  class  of  birds  had  ever  been  able  to  have 
crossed  the  Atlantic  Ocean.  Thus,  on  the  theory  of 
evolution,  we  can  well  understand  the  second  corre- 
lation now  before  us — namely,  between  remoteness 
of  affinity  and  generality  of  dispersal, — so  that 
there  is  no  considerable  portion  of  the  habitable 
globe  without  representatives  of  all  the  classes  of 
animals,  few  portions  without  representatives  of  all 
the  orders,  but  many  portions  without  many  of  the 
families,  innumerable  portions  without  innumerable 
genera,  and,  of  course,  all  portions  without  the  great 
majority  of  species.  Now,  while  this  general  correla- 
tion thus  obviously  supports  the  theory  of  natural 
descent  with  progressive  modification,  it  makes  di- 
rectly against  the  opposite  theory  of  special  creation. 
For  we  have  recently  seen  that  when  we  restrict  our 
view  to  the  case  of  species  and  genera,  the  theory  of 
special  creation  is  obliged  to  suppose  that  for  some 
inscrutable  reason  the  Deity  had  regard  to  systematic 
affinity  while  determining  on  what  laige  aieas  to 


216  Darwin,  and  after  Darwin. 

create  his  species l.  But  now  we  see  that  he  must 
be  held  to  have  neglected  this  inscrutable  reason 
(whatever  it  was)  when  he  passed  beyond  the  range 
of  genera — and  this  always  in  proportion  to  the  re- 
moteness of  systematic  affinity  on  the  part  of  the 
species  concerned. 

I  cannot  well  conceive  a  rednctio  ad  absurdnm 
more  complete  than  this.  But,  having  now  presented 
these  most  general  facts  of  geographical  distribution 
in  their  relation  to  the  issue  before  us,  we  may  next 
proceed  to  consider  a  few  illustrations  of  them  in 
detail,  for  in  this  way  I  think  that  their  overwhelming 
weight  may  become  yet  more  abundantly  apparent. 

It  will  assist  us  in  dealing  with  these  detailed  illus- 
trations if  we  begin  by  considering  the  means  of 
dispersal  of  organisms  from  one  place  to  another. 
Of  course  the  most  ordinary  means  is  that  of  con- 
tinuous wandering,  or  emigration  ;  but  where  geo- 
graphical barriers  of  any  kind  have  to  be  surmounted, 
organisms  may  only  be  able  to  pass  them  by  more 
exceptional  and  accidental  means.  The  principal 
barriers  of  a  geographical  kind  are  oceans,  rivers, 
mountain-chains,  and  desert-tracts,  in  the  case  of 


1  I  say  "large  areas"  for  the  sake  of  argument;  but  the  same  cor- 
relation between  distribution  and  affinity  extends  likewise  to  small 
areas  where  only  small  differences  of  affinity  are  concerned.  Thns, 
for  instance,  speaking  of  smaller  areas,  Moritz  Wagner  says : — "  The 
broader  and  more  rapid  the  river,  the  higher  and  more  regular  the 
mountain-chain,  the  calmer  and  more  extensive  the  sea,  the  more 
considerable,  as  a  general  rule,  will  be  the  taxonomic  separation  be- 
tween the  populations " ;  and  he  shows  that,  in  correlation  with  such 
differences  in  the  degrees  of  separation,  are  the  degrees  of  diversification — 
i.  e.,  the  numbers  of  species,  and  even  of  varieties,  which  these  topo- 
graphical barriers  determine. 


Geographical  Distribution.  217 

terrestrial  organisms ;  and,  in  the  case  of  aquatic 
organisms,  the  presence  of  land.  But  it  is  to  be 
observed  that,  as  regards  marine  organisms,  any  con- 
siderable difference  in  the  temperature  of  the  water 
may  constitute  a  barrier  as  effectual  as  the  presence 
of  land  ;  and  also  that,  in  the  case  of  all  shallow- 
water  faunas,  a  tract  of  deep  ocean  constitutes  almost 
as  complete  a  barrier  as  it  does  to  terrestrial  faunas. 

Now,  the  means  whereby  barriers  admit  of  being 
accidentally  or  occasionally  surmounted  are,  of  course, 
various;  and  they  differ  in  the  case  of  different 
organisms.  Birds,  bats,  and  insects,  on  account  of 
their  powers  of  flight,  are  particularly  apt  to  be  blown 
out  great  distances  to  sea,  and  hence  of  all  animals 
are  most  likely  to  become  the  involuntary  colonists  of 
distant  shores.  Floating  timber  serves  to  convey 
seeds  and  eggs  of  small  animals  over  great  distances  ; 
and  Darwin  has  shown  that  many  kinds  of  seeds  are 
able  of  themselves  to  float  for  more  than  a  month  in 
sea- water  without  losing  their  powers  of  germination. 
For  instance,  out  of  87  kinds,  64  germinated  after  an 
immersion  of  28  days,  and  a  few  survived  an  immersion 
of  137  days.  As  a  result  of  all  his  experiments  he 
concludes,  that  the  seeds  of  at  least  ten  per  cent,  of  the 
species  of  plants  of  any  country  might  be  floated  by 
sea-currents  during  28  days,  without  losing  their 
powers  of  germination  ;  and  this,  at  the  average  rate 
of  flow  of  several  Atlantic  currents,  would  serve  to 
transport  the  seeds  to  a  distance  of  at  least  900  miles. 
Again,  he  proved  that  even  seeds  which  are  quickly 
destroyed  by  contact  with  sea-water  admit  of  being 
successfully  transported  during  30  days,  if  they  be 
contained  within  the  crop  of  a  dead  bird.  He  also 


218          Darwin,  and  after  Darwin. 

proved  that  living  birds  are  most  active  agents  in  the 
work  of  dissemination,  and  this  not  only  by  taking 
seeds  into  their  crops  (where,  so  long  as  they  remain, 
the  seeds  are  uninjured),  but  likewise  by  carrying  seeds 
(and  even  young  mollusks)  attached  to  their  feet  and 
feathers.  In  the  course  of  these  experiments  he  found 
that  a  small  cup-full  of  mud,  which  he  gathered  from 
the  edges  of  three  ponds  in  February,  was  so  charged 
with  seeds  that  when  sown  in  the  ground  these  few 
ounces  of  mud  yielded  no  less  than  537  plants,  belong- 
ing to  many  different  species.  It  is  therefore  evident 
what  opportunities  are  thus  afforded  for  the  trans- 
portation of  seeds  on  the  feet  and  bills  of  wading-birds. 
Lastly,  floating  ice  is  well  known  to  act  as  a  carrier 
of  any  kind  of  life  which  may  prove  able  to  survive 
this  mode  of  transit. 

Such  being  the  nature  of  geographical  barriers,  and 
the  means  that  organisms  of  various  kinds  may 
occasionally  have  of  overcoming  them,  I  will  now  give 
a  few  detailed  illustrations  of  the  argument  from 
geographical  distribution,  as  previously  presented  in 
its  general  form. 

To  begin  with  aquatic  animals.  As  Darwin  remarks, 
'•  the  marine  inhabitants  of  the  Eastern  and  Western 
shores  of  South  America  are  very  distinct ;  with 
extremely  few  shells,  Crustacea,  or  echinodermata  in 
common."  Again,  westward  of  the  shores  of  America, 
a  wide  space  of  open  ocean  extends,  which,  as  we 
have  seen,  furnishes  as  effectual  a  barrier  as  does  the 
land  to  any  emigration  of  shallow-water  animals. 
Now,  as  soon  as  this  reach  of  deep  water  is  passed,  we 
meet  in  the  eastern  islands  of  the  Pacific  with  another 
and  totally  distinct  fauna.  "So  that  three  marine 


Geographical  Distribution.  219 

faunas  range  northward  and  southward  in  parallel 
lines  not  far  from  each  other,  under  corresponding 
climates  "  :  they  are,  however,  "  separated  from  each 
other  by  impassable  barriers,  either  of  land  or  open 
sea  "  :  and  it  is  in  exact  coincidence  with  the  course  of 
these  barriers  that  we  find  so  remarkable  a  differen- 
tiation of  the  faunas1.  Obviously,  therefore,  it  is 
impossible  to  suggest  that  this  correlation  is  accidental. 
Altogether  many  thousands  of  species  are  involved, 
and  within  this  comparatively  limited  area  they  are 
sharply  marked  off  into  three  groups  as  to  their 
natural  affinities,  and  into  three  groups  as  to  their 
several  basins.  Hence,  if  all  these  species  were 
separately  created,  there  is  no  escape  from  the  con- 
clusion that  for  some  reason  or  another  the  act  of 
creation  was  governed  by  the  presence  of  these 
barriers,  so  that  species  deposited  on  the  Eastern 
shores  of  South  America  were  formed  with  one  set  of 
natural  affinities,  while  species  deposited  on  the 
Western  shore  were  formed  with  another  set;  and 
similarly  with  regard  to  the  third  set  of  species  in  the 
third  basin,  which,  extending  over  a  whole  hemisphere 
to  the  coast  of  Africa  without  any  further  barrier, 
nowhere  presents,  over  this  vast  area,  any  other  case 
of  a  distinct  marine  fauna.  But  what  conceivable 
reason  can  there  have  been  thus  to  consult  these 
geographical  barriers  in  the  original  creation  of  specific 

The  only  exception  is  in  the  case  of  the  fish  on  each  side  of  the 
Isthmus  of  Panama,  where  about  30  per  cent,  of  the  species  are  identi- 
cal. But  it  is  possible  enough  that  at  some  previous  time  this  narrow 
isthmus  may  have  been  even  narrower  than  at  present,  if  not  actually 
open.  At  all  events,  the  fact  that  this  partial  exception  occurs  just 
where  the  land-barrier  is  so  narrow,  is  more  suggestive  of  migration 
than  of  independent  creation. 


220  Darwin,  and  after  Darwin. 

types  ?  Even  if  such  a  case  stood  alone,  it  would  be 
strongly  suggestive  of  error  on  the  part  of  the  special 
creation  theory.  But  let  us  take  another  case,  this 
time  from  fresh-water  faunas. 

Although  the  geographical  distribution  of  fresh- 
water fish  and  fresh-water  shells  is  often  surprisingly 
extensive  and  apparently  capricious,  this  may  be 
explained  by  the  means  of  dispersal  being  here  so 
varied— not  only  aquatic  birds,  floods,  and  whirl- 
winds, but  also  geographical  changes  of  water-shed 
having  all  assisted  in  the  process.  Moreover,  in 
some  cases  it  is  possible  that  the  habits  of  more 
widely  distributed  fresh-water  fish  may  have  origin- 
ally been  wholly  or  partly  marine — which,  of  course, 
would  explain  the  existing  discontinuity  of  their  ex- 
isting fresh-water  distribution.  But,  be  this  as  it 
may  (and  it  is  not  a  question  that  affects  the  issue 
between  special  creation  and  gradual  evolution,  since 
it  is  only  a  question  as  to  how  a  given  species  has 
been  dispersed  from  its  original  home,  whether  or 
not  in  that  home  it  was  specially  .created),  the 
point  I  desire  to  bring  forward  is,  that  where  we 
find  a  barrier  to  the  emigration  of  fresh-water 
forms  which  is  more  formidable  than  a  thousand 
miles  of  ocean — a  barrier  over  which  neither 
water-fowl  nor  whirlwinds  are  likely  to  pass,  and 
which  is  above  the  reach  of  any  geological  changes 
of  water-shed, — where  we  find  such  a  barrier,  we 
always  find  a  marked  difference  in  the  fresh-water 
faunas  on  either  side  of  it.  The  kind  of  barrier 
to  which  I  allude  is  a  high  mountain-chain.  It 
may  be  only  a  few  miles  wide  ;  yet  it  exercises  a 
greater  influence  on  the  diversification  of  specific 


Geographical  Distribution.  221 

types,  where  fresh-water  faunas  are  concerned,  than 
almost  any  other.  But  why  should  this  be  the  case 
on  any  intelligible  theory  of  special  creation  ?  Why, 
in  the  depositing  of  species  of  newly  created  fresh- 
water fish,  should  the  presence  of  an  impassable 
mountain-chain  have  determined  so  uniformly  a  dif- 
ference of  specific  affinity  on  either  side  of  it  ?  The 
question,  so  far  as  I  can  see,  does  not  admit  of  an 
answer  from  any  reasonable  opponent. 

Turning  now  from  aquatic  organisms  to  terrestrial, 
the  body  of  facts  from  which  to  draw  is  so  large, 
that  I  think  the  space  at  my  disposal  may  be  best 
utilized  by  confining  attention  to  a  single  division 
of  them — that,  namely,  which  is  furnished  by  the 
zoological  study  of  oceanic  islands. 

In  the  comparatively  limited — but  in  itself  extensive 
— class  of  facts  thus  presented,  we  have  a  particularly 
fair  and  cogent  test  as  between  the  alternative  theories 
of  evolution  and  creation.  For  where  we  meet  with  a 
volcanic  island,  hundreds  of  miles  from  any  other  land, 
and  rising  abruptly  from  an  ocean  of  enormous  depth, 
we  may  be  quite  sure  that  such  an  island  can  never 
have  formed  part  of  a  now  submerged  continent.  In 
other  words,  we  may  be  quite  sure  that  it  always  has 
been  what  it  now  is — an  oceanic  peak,  separated 
from  all  other  land  by  hundreds  of  miles  of  sea, 
and  therefore  an  area  supplied  by  nature  for  the 
purpose,  as  it  were,  of  testing  the  rival  theories  of 
creation  and  evolution.  For,  let  us  ask,  upon  these 
tiny  insular  specks  of  land  what  kind  of  life  should 
we  expect  to  find?  To  this  question  the  theories 
of  special  creation  and  of  gradual  evolution  would 


222  Darwin,  and  after  Darwin. 

agree  in  giving  the  same  answer  up  to  a  certain 
point.  For  both  theories  would  agree  in  supposing 
that  these  islands  would,  at  all  events  in  large  part, 
derive  their  inhabitants  from  accidental  or  occasional 
arrivals  of  wind-blown  or  water-floated  organisms 
from  other  countries — especially,  of  course,  from  the 
countries  least  remote.  But,  after  agreeing  upon 
this  point,  the  two  theories  must  part  company  in 
their  anticipations.  The  special-creation  theory  can 
have  no  reason  to  suppose  that  a  small  volcanic 
island  in  the  midst  of  a  great  ocean  should  be  chosen 
as  the  theatre  of  any  extraordinary  creative  activity, 
or  for  any  particularly  rich  manufacture  of  peculiar 
species  to  be  found  nowhere  else  in  the  world.  On 
the  other  hand,  the  evolution  theory  would  expect 
to  find  that  such  habitats  are  stocked  with  more  or 
less  peculiar  species.  For  it  would  expect  that  when 
any  organisms  chanced  to  reach  a  wholly  isolated 
refuge  of  this  kind,  their  descendants  should  forth- 
with have  started  upon  an  independent  course  of 
evolutionary  history.  Protected  from  intercrossing 
with  any  members  of  their  parent  species  elsewhere, 
and  exposed  to  considerable  changes  in  their  con- 
ditions of  life,  it  would  indeed  be  fatal  to  the 
general  theory  of  evolution  if  these  descendants, 
during  the  course  of  many  generations,  were  not  to 
undergo  appreciable  change.  It  has  happened  on 
two  or  three  occasions  that  European  rats  have  been 
accidentally  imported  by  ships  upon  some  of  these 
islands,  and  even  already  it  is  observed  that  their 
descendants  have  undergone  a  slight  change  of  ap- 
pearance, so  as  to  constitute  them  what  naturalists 
call  local  varieties.  The  change,  of  course,  is  but 


Geographical  Distribution.  223 

slight,  because  the  time  allowed  for  it  has  been  so 
short.  But  the  longer  the  time  that  a  colony  of  a 
species  is  thus  completely  isolated  under  changed 
conditions  of  life,  the  greater,  according  to  the  evolu- 
tion theory,  should  we  expect  the  change  to  become. 
Therefore,  in  all  cases  where  we  happen  to  know, 
from  independent  evidence  of  a  geological  kind,  that 
an  oceanic  island  is  of  very  ancient  formation,  the 
evolution  theory  would  expect  to  encounter  a 
great  wealth  of  peculiar  species.  On  the  other 
hand,  as  I  have  just  observed,  the  special-creation 
theory  can  have  no  reason  to  suppose  that  there 
should  be  any  correlation  between  the  age  of  an 
oceanic  island  and  the  number  of  peculiar  species 
which  it  may  be  found  to  contain. 

Therefore,  having  considered  the  principles  of  geo- 
graphical distribution  from  the  widest  or  most  general 
point  of  view,  we  shall  pass  to  the  opposite  extreme, 
and  consider  exhaustively,  or  in  the  utmost  possible 
detail,  the  facts  of  such  distribution  where  the  con- 
ditions are  best  suited  to  this  purpose— that  is,  as  I 
have  already  said,  upon  oceanic  islands,  which  may  be 
metaphorically  regarded  as  having  been  formed  by 
nature  for  the  particular  purpose  of  supplying  natura- 
lists with  a  crucial  test  between  the  theories  of 
creation  and  evolution.  The  material  upon  which  my 
analysis  is  to  be  based  will  be  derived  from  the  most 
recent  works  upon  geographical  distribution— espe- 
cially from  the  magnificent  contributions  to  this  depart- 
ment of  science  which  we  owe  to  the  labours  of  Mr. 
Wallace.  Indeed,  all  that  follows  may  be  regarded  as 
a  condensed  nitrate  of  the  facts  which  he  has  collected. 
Even  as  thus  restricted,  however,  our  subject-matter 


224  Darwin,  and  after  Darwin. 

would  be  too  extensive  to  be  dealt  with  on  the  pre- 
sent occasion,  were  we  to  attempt  an  exhaustive  ana- 
lysis of  the  floras  and  faunas  of  all  oceanic  islands 
upon  the  face  of  the  globe.  Therefore,  what  I  pro- 
pose to  do  is  to  select  for  such  exhaustive  analysis  a 
few  of  what  may  be  termed  the  most  oceanic  of 
oceanic  islands — that  is  to  say,  those  oceanic  islands 
which  are  most  widely  separated  from  mainlands, 
and  which,  therefore,  furnish  the  most  unquestionable 
of  test  cases  as  between  the  theories  of  special  crea- 
tion and  genetic  descent. 

Azores. — A  group  of  volcanic  islands,  nine  in  num- 
ber, about  900  miles  from  the  coast  of  Portugal, 
and  surrounded  by  ocean  depths  of  1,800  to  2,500 
fathoms.  There  is  geological  evidence  that  the  origin 
of  the  group  dates  back  at  least  as  far  as  Miocene 
times.  There  is  a  total  absence  of  all  terrestrial  Ver- 
tebrata,  other  than  those  which  are  known  to  have  been 
introduced  by  man.  Flying  animals,  on  the  other  hand, 
are  abundant ;  namely,  53  species  of  birds,  one  species 
of  bat,  a  few  species  of  butterflies,  moths,  and  hymenop- 
tera,  with  74  species  of  indigenous  beetles.  All  these 
animals  are  unmodified  European  species,  with  the 
exception  of  one  bird  and  many  of  the  beetles.  Of 
the  74  indigenous  species  of  the  latter,  36  are  not 
found  in  Europe  ;  but  19  are  natives  of  Madeira  or 
the  Canaries,  and  3  are  American,  doubtless  trans- 
planted by  drift-wood.  The  remaining  14  species 
occur  nowhere  else  in  the  world,  though  for  the  most 
part  they  are  allied  to  other  European  species.  There 
are  69  known  species  of  land-shells,  of  which  37  are 
European,  and  32  peculiar,  though  all  allied  to  Euro- 


Geographical  Distribution.  225 

pean  forms.  Lastly,  there  are  480  known  species  of 
plants,  of  which  40  are  peculiar,  though  allied  to 
European  species. 

Bermudas. — A  small  volcanic  group  of  islands,  700 
miles  from  North  Carolina.  Although  there  are 
about  100  islands  in  the  group,  their  total  area  does 
not  exceed  50  square  miles.  The  group  is  surrounded 
by  water  varying  in  depth  from  2,500  to  3,800  fathoms. 
The  only  terrestrial  Vertebrate  (unless  the  rats  and 
mice  are  indigenous)  is  a  lizard  allied  to  an  American 
form,  but  specifically  distinct  from  it,  and  therefore  a 
solitary  species  which  does  not  occur  anywhere  else  in 
the  world.  None  of  the  birds  or  bats  are  peculiar, 
any  more  than  in  the  case  of  the  Azores  ;  but,  as  in 
that  case,  a  large  percentage  of  the  land-shells  are  so 
— namely,  at  least  one  quarter  of  the  whole.  Neither 
the  botany  nor  the  entomology  of  this  group  has  been 
worked  out  ;  but  I  have  said  enough  to  show  how  re- 
markably parallel  are  the  cases  of  these  two  volcanic 
groups  of  islands  situated  in  different  hemispheres,  but 
at  about  the  same  distance  from  large  continents.  In 
both  there  is  an  extraordinary  paucity  of  terrestrial 
vertebrata,  and  of  any  peculiar  species  of  bird  or  beast. 
On  the  other  hand,  there  is  in  both  a  marvellous 
wealth  of  peculiar  species  of  insects  and  land-shells. 
Now  these  correlations  are  all  abundantly  intelligible. 
It  is  a  difficult  matter  for  any  terrestrial  animal  to 
cross  900,  or  even  700,  miles  of  ocean  :  therefore  only 
one  lizard  has  succeeded  in  doing  so  in  one  of  the  two 
parallel  cases ;  and,  living  cut  off  from  intercrossing 
with  its  parent  form,  the  descendants  of  that  lizard 
have  become  modified  so  as  to  constitute  a  peculiar 
species.  But  it  is  more  easy  for  large  flying  animals 

*  Q 


226          Darwin,  and  after  Farwin. 

to  cross  those  distances  of  ocean  :  consequently,  there 
is  only  one  instance  of  a  peculiar  species  of  bird  or 
bat — namely,  a  bull-finch  in  the  Azores,  which,  being  a 
small  land-bird,  is  not  likely  ever  to  have  had  any 
other  visitors  from  its  original  parent  species  coming 
over  from  Europe  to  keep  up  the  original  breed. 
Lastly,  it  is  very  much  more  easy  for  insects  and 
land-mollusca  to  be  conveyed  to  such  islands  by  wind 
and  floating  timber  than  it  is  for  terrestrial  mammals, 
or  even  than  it  is  for  small  birds  and  bats  ;  but  yet 
such  means  of  transit  are  not  sufficiently  sure  to  admit 
of  much  recruiting  from  the  mainland  for  the  purpose 
of  keeping  up  the  specific  types.  Consequently,  the 
insects  and  the  land-shells  present  a  much  greater 
proportion  of  peculiar  species — namely,  one  half  and 
one  fourth  of  the  land-shells  in  the  one  case,  and 
one  eighth  of  the  beetles  in  the  other.  All  these 
correlations,  I  say,  are  abundantly  intelligible  on  the 
theory  of  evolution ;  but  who  shall  explain,  on  the 
opposite  theory,  why  orders  of  beetles  and  land-mol- 
lusca should  have  been  chosen  from  among  all  other 
animals  for  such  superabundant  creation  on  oceanic 
islands,  so  that  in  the  Azores  alone  we  find  no  less 
than  32  of  the  one  and  14  of  the  other  ?  And,  in  this 
connexion,  I  may  again  allude  to  the  peculiar  species 
of  beetles  in  the  island  of  Madeira.  Here  there  are 
an  enormous  number  of  peculiar  species,  though  they 
are  nearly  all  related  to,  or  included  under  the  same 
genera  as,  beetles  on  the  neighbouring  continent. 
Now,  as  we  have  previously  seen,  no  less  than 
200  of  these  species  have  lost  the  use  of  their 
wings.  Evolutionists  explain  this  remarkable  fact 
by  their  general  laws  of  degeneration  under  disuse, 


Geographical  Distribution.  227 

and  the  operation  of  natural  selection,  as  will  be 
shown  later  on  ;  but  it  is  not  so  easy  for  special 
creationists  to  explain  why  this  enormous  number 
of  peculiar  species  of  beetles  should  have  been 
deposited  on  Madeira,  all  allied  to  beetles  on  the 
nearest  continent,  and  nearly  all  deprived  of  the 
use  of  their  wings.  And  similarly,  of  course,  with 
all  the  peculiar  species  of  the  Bermudas  and  the 
Azores.  For  who  will  explain,  on  the  theory 
of  independent  creation,  why  all  the  peculiar  species, 
both  of  animals  and  plants,  which  occur  on  the  Ber- 
mudas should  so  unmistakably  present  American 
affinities,  while  those  which  occur  on  the  Azores 
no  less  unmistakably  present  European  affinities? 
But  to  proceed  to  other,  and  still  more  remarkable, 
cases. 

The  Galapagos  Islands. — This  archipelago  is  of 
volcanic  origin,  situated  under  the  equator  between 
500  and  600  miles  from  the  West  Coast  of  South 
America.  The  depth  of  the  ocean  around  them 
varies  from  2,oco  to  3,000  fathoms  or  more.  This 
group  is  of  particular  interest,  from  the  fact  that 
it  was  the  study  of  its  fauna  which  first  sug- 
gested to  Darwin's  mind  the  theory  of  evolution. 
I  will,  therefore,  begin  by  quoting  a  short  passage 
from  his  writings  upon  the  zoological  relations  of 
this  particular  fauna. 

Here  almost  every  product  of  the  land  and  of  the  water  bears 
the  unmistakeable  stamp  of  the  American  continent.  There 
are  twenty-six  land  birds;  of  these,  twenty-one,  or  perhaps 
twenty-three,  are  ranked  as  distinct  species,  and  would  com- 
monly be  assumed  to  have  been  here  created;  yet  the  close 
affinity  of  most  of  these  birds  to  American  species  is  manifest  in 
every  character,  in  their  habits,  gestures,  and  tones  of  voice. 
Q2 


228          Darwin,  and  after  Darwin. 

So  it  is  with  the  other  animals,  and  with  a  large  proportion  of 
the  plants,  as  shown  by  Dr.  Hooker  in  his  admirable  Flora  of 
this  archipelago.  The  naturalist,  looking  at  the  inhabitants 
of  these  volcanic  islands  in  the  Pacific,  distant  several  hundred 
miles  from  the  continent,  feels  that  he  is  standing  on  American 
land.  Why  should  this  be  so  ?  Why  should  the  species  which 
are  supposed  to  have  been  created  in  the  Galapagos  Archi- 
pelago, and  nowhere  else,  bear  so  plainly  the  stamp  of  affinity 
to  those  created  in  America?  There  is  nothing  in  the  con- 
ditions of  life,  in  the  geological  nature  of  the  islands,  in  their 
height  or  climate,  or  in  the  proportions  in  which  the  several 
classes  are  associated  together,  which  closely  resembles  the 
conditions  of  the  South  American  coast ;  in  fact,  there  is  a 
considerable  dissimilarity  in  all  these  respects.  On  the  other 
hand,  there  is  a  considerable  degree  of  resemblance  in  the 
volcanic  nature  of  the  soil,  in  the  climate,  height,  and  size  of 
the  islands,  between  the  Galapagos  and  Cape  de  Verde  Archi- 
pelagoes ;  but  what  an  entire  and  absolute  difference  in  their 
inhabitants!  The  inhabitants  of  the  Cape  de  Verde  Islands 
are  related  to  those  of  Africa,  like  those  of  the  Galapagos  to 
America.  Facts  such  as  these  admit  of  no  sort  of  explanation 
on  the  ordinary  view  of  independent  creation ;  whereas  on  the 
view  here  maintained,  it  is  obvious  that  the  Galapagos  Islands 
would  be  likely  to  receive  colonists  from  America,  and  the  Cape 
de  Verde  Islands  from  Africa  ;  such  colonists  would  be  liable  to 
modification— the  principle  of  inheritance  still  betraying  their 
original  birthplace l. 

The  following  is  a  synopsis  of  the  fauna  and  flora 
of  this  archipelago,  so  far  as  at  present  known.  The 
only  terrestrial  vertebrates  are  two  peculiar  species 
of  land-tortoise,  and  one  extinct  species  ;  five  species 
of  lizards,  all  peculiar — two  of  them  so  much  so 
as  to  constitute  a  peculiar  genus ; — and  two  species 
of  snakes,  both  closely  allied  to  South  American 
forms.  Of  birds  there  are  57  species,  of  which  no 

1  Origin  of  Species,  pp.  353~4- 


Geographical  Distribution.  229 

less  than  38  are  peculiar  ;  and  all  the  non-peculiar 
species,  except  one,  belong  to  aquatic  tribes.  The 
true  land- birds  are  represented  by  31  species,  of 
which  all,  except  one,  are  peculiar  ;  while  more  than 
half  of  them  go  to  constitute  peculiar  genera.  More- 
over, while  they  are  all  unquestionably  allied  to 
South  American  forms,  they  present  a  beautiful 
series  of  gradations,  "  from  perfect  identity  with  the 
continental  species,  to  genera  so  distinct  that  it  is 
difficult  to  determine  with  what  forms  they  are  most 
nearly  allied  ;  and  it  is  interesting  to  note  that  this 
diversity  bears  a  distinct  relation  to  the  probabilities 
of,  and  facilities  for,  migration  to  the  islands.  The 
excessively  abundant  rice-bird,  which  breeds  in 
Canada,  and  swarms  over  the  whole  United  States, 
migrating  to  the  West  Indies  and  South  America, 
visiting  the  distant  Bermudas  almost  every  year, 
and  extending  its  range  as  far  as  Paraquay,  is  the 
only  species  of  land-bird  which  remains  completely 
unchanged  in  the  Galapagos  ;  and  we  may  therefore 
conclude  that  some  stragglers  of  the  migrating  host 
reach  the  islands  sufficiently  often  to  keep  up  the 
purity  of  the  breed  1."  Again,  of  the  thirty  peculiar 
land-birds,  it  is  observable  that  the  more  they  differ 
from  any  other  species  or  genera  on  the  South 
American  continent,  the  more  certainly  are  they  found 
to  have  their  nearest  relations  among  those  South 
American  forms  which  have  the  more  restricted 
range,  and  are  therefore  the  least  likely  to  have  found 
their  way  to  the  islands  with  any  frequency. 

The  insect  fauna  of  the  Galapagos  islands  is  scanty, 
and  chiefly  composed  of  beetles.     These  number  35 

1  Wallace,  Island  Life,  pp.  271-3. 


230          Darwin,  and  after  Darwin. 

species,  which  are  nearly  all  peculiar,  and  in  some 
cases  go  to  constitute  peculiar  genera.  The  same 
remarks  apply  to  the  twenty  species  of  land-shells. 
Lastly,  of  the  total  number  of  flowering  plants  (332 
species)  more  than  one  half  (174  species)  are  pecu- 
liar. It  is  observable  in  the  case  of  these  peculiar 
species  of  plants— as  also  of  the  peculiar  species  of 
birds — that  many  of  them  are  restricted  to  single 
islands.  It  is  also  observable  that,  with  regard  both 
to  the  fauna  and  flora,  the  Galapagos  Islands  as  a 
whole  are  very  much  richer  in  peculiar  species  than 
either  the  Azores  or  Bermudas,  notwithstanding 
that  both  the  latter  are  considerably  more  remote 
from  their  nearest  continents.  This  difference,  which 
at  first  sight  appears  to  make  against  the  evolu- 
tionary interpretation,  really  tends  to  confirm  it. 
For  the  Galapagos  Islands  are  situated  in  a  calm 
region  of  the  globe,  unvisited  by  those  periodic 
storms  and  hurricanes  which  sweep  over  the  North 
Atlantic,  and  which  every  year  convey  some  strag- 
gling birds,  insects,  seeds,  &c.,  to  the  Azores  and 
Bermudas.  Notwithstanding  their  somewhat  greater 
isolation  geographically,  therefore,  the  Azores  and 
Bermudas  are  really  less  isolated  biologically  than 
are  the  Galapagos  Islands  ;  and  hence  the  less  degree 
of  peculiarity  on  the  part  of  their  endemic  species. 
But,  on  the  theory  of  special  creation,  it  is  impos- 
sible to  understand  why  there  should  be  any  such 
correlation  between  the  prevalence  of  gales  and  a 
comparative  inertness  of  creative  activity.  And,  as 
we  have  seen,  it  is  equally  impossible  on  this  theory 
to  understand  why  there  should  be  a  further  corre- 
lation between  the  degree  of  peculiarity  on  the  part 


Geographical  Distribution.  231 

of  the  isolated  species,  and  the  degree  in  which  their 
nearest  allies  on  the  mainland  are  there  confined 
to  narrow  ranges,  and  therefore  less  likely  to  keep 
up  any  biological  communication  with  the  islands. 

St.  Helena. — A  small  volcanic  island,  ten  miles  long 
by  eight  wide,  situated  in  mid-ocean,  uoo  miles  from 
Africa,  and  1800  from  South  America.  It  is  very 
mountainous  and  rugged,  bounded  for  the  most  part 
by  precipices,  rising  from  ocean  depths  of  17000  feet, 
to  a  height  above  the  sea-level  of  nearly  3,000. 
When  first  discovered  it  was  richly  clothed  with 
forests ;  but  these  were  all  destroyed  by  human 
agency  during  the  i6th,  i;th  and  i8th  centuries. 
The  records  of  civilization  present  no  more  lament- 
able instance  of  this  kind  of  destruction.  From  a 
merely  pecuniary  point  of  view  the  abolition  of 
these  primeval  forests  has  proved  an  irreparable 
loss  ;  but  from  a  scientific  point  of  view  the  loss 
is  incalculable.  These  forests  served  to  harbour 
countless  forms  of  life,  which  extended  at  least  from 
the  Miocene  age,  and  which,  having  found  there  an 
ocean  refuge,  survived  as  the  last  remnants  of  a  remote 
geological  epoch.  In  those  days,  as  Mr.  Wallace 
observes,  St.  Helena  must  have  formed  a  kind  of 
natural  museum  or  vivarium  of  archaic  species  of  all 
classes,  the  interest  of  which  we  can  now  only  surmise 
from  the  few  remnants  of  those  remnants,  which  are 
still  left  among  the  more  inaccessible  portions  of  the 
mountain  peaks  and  crater  edges.  These  remnants 
of  remnants  are  as  follows. 

There  is  a  total  absence  of  all  indigenous  mam- 
mals, reptiles,  fresh-water  fish,  and  true  land-birds. 
There  is,  however,  a  species  of  plover,  allied  to  one 


232          Darwin,  and  after  Darwin. 

in  South  Africa ;  but  it  is  specifically  distinct,  and 
therefore  peculiar  to  the  island.  The  insect  life,  on 
the  other  hand,  is  abundant.  Of  beetles  no  less  than 
129  species  are  believed  to  be  aboriginal,  and,  with 
one  single  exception,  the  whole  number  are  peculiar 
to  the  island.  "  But  in  addition  to  this  large  amount 
of  specific  peculiarity  (perhaps  unequalled  anywhere 
else  in  the  world),  the  beetles  of  this  island  are 
remarkable  for  their  generic  isolation,  and  for  the 
altogether  exceptional  proportion  in  which  the  great 
divisions  of  the  order  are  represented.  The  species 
belong  to  39  genera,  of  which  no  less  than  25  are 
peculiar  to  the  island  ;  and  many  of  these  are  such 
isolated  forms  that  it  is  impossible  to  find  their 
allies  in  any  particular  country  V  More  than  two- 
thirds  of  all  the  species  belong  to  the  group  of 
weevils — a  circumstance  which  serves  to  explain  the 
great  wealth  of  beetle-population,  the  weevils  being 
beetles  which  live  in  wood,  and  St.  Helena  having 
been  originally  a  densely  wooded  island.  This  cir- 
cumstance is  also  in  accordance  with  the  view  that 
the  peculiar  insect  fauna  has  been  in  large  part 
evolved  from  ancestors  which  reached  the  island  by 
means  of  floating  timber  ;  for,  of  course,  no  explana- 
tion can  be  suggested  why  special  creation  of  this 
highly  peculiar  insect  fauna  should  have  run  so  dis- 
proportionately into  the  production  of  weevils.  About 
two-thirds  of  the  whole  number  of  beetles,  or  over 
80  species,  show  no  close  affinity  with  any  existing 
insects,  while  the  remaining  third  have  some  rela- 
tions, though  often  very  remote,  with  European  and 
African  forms.  That  this  high  degree  of  peculiarity 

1  Wallace,  Island  Life,  p.  287. 


Geographical  Distribution.  233 

is  due  to  high  antiquity  is  further  indicated,  accord- 
ing to  our  theory,  by  the  large  number  of  species  which 
some  of  the  types  comprise.  Thus,  the  54  species  of 
Cossonidx  may  be  referred  to  three  types  ;  the  1 1 
species  of  Bembidium  form  a  group  by  themselves  ; 
and  the  Heteromera  form  two  groups.  "  Now,  each 
of  these  types  may  well  be  descended  from  a  single 
species,  which  originally  reached  the  island  from 
some  other  land  ;  and  the  great  variety  of  generic 
and  specific  forms  into  which  some  of  them  have 
diverged  is  an  indication,  and  to  some  extent  a 
measure,  of  the  remoteness  of  their  origin  1."  But, 
on  the  counter-supposition  that  all  these  128  pecu- 
liar species  were  separately  created  to  occupy  this 
particular  island,  it  is  surely  unaccountable  that  they 
should  thus  present  such  an  arborescence  of  natural 
affinities  amongst  themselves. 

Passing  over  the  rest  of  the  insect  fauna,  which  has 
not  yet  been  sufficiently  worked  out,  we  next  find  that 
there  are  only  20  species  of  indigenous  land-shells — 
which  is  not  surprising  when  we  remember  by  what 
enormous  reaches  of  ocean  the  island  is  surrounded. 
Of  these  20  species  no  less  than  13  have  become 
extinct,  three  are  allied  to  European  species,  while 
the  rest  are  so  highly  peculiar  as  to  have  no 
near  allies  in  any  other  part  of  the  globe.  So  that 
the  land-shells  tell  exactly  the  same  story  as  the 
insects. 

Lastly,  the  plants  likewise  tell  the  same  story. 
The  truly  indigenous  flowering  plants  are  about  5° 
in  number,  besides  26  ferns.  Forty  of  the  former 
and  ten  of  the  latter  are  peculiar  to  the  island, 

1  Wallace,  Island  Life,  p.  287. 


234          Darwin,  and  after  Darwin. 

and,  as  Sir  Joseph  Hooker  tells  us,  "  cannot  be  re- 
garded as  very  close  specific  allies  of  any  other  plants 
at  all."  Seventeen  of  them  belong  to  peculiar  genera, 
and  the  others  all  differ  so  markedly  as  species  from 
their  congeners,  that  not  one  comes  under  the  cate- 
gory of  being  an  insular  form  of  a  continental  species. 
So  that  with  respect  to  its  plants  no  less  than  with 
respect  to  its  animals,  we  find  that  the  island  of 
St.  Helena  constitutes  a  little  world  of  unique  species, 
allied  among  themselves,  but  diverging  so  much  from 
all  other  known  forms  that  in  many  cases  they  con- 
stitute unique  genera. 

Sandwich  Islands. — These  are  an  extensive  group 
of  islands,  larger  than  any  we  have  hitherto  con- 
sidered—the largest  of  the  group  being  about  the  size 
of  Devonshire.  The  entire  archipelago  is  volcanic, 
with  mountains  rising  to  a  height  of  nearly  14,000 
feet.  The  group  is  situated  in  the  middle  of  the  North 
Pacific,  at  a  distance  of  considerably  over  2,000  miles 
from  any  other  land,  and  surrounded  by  enormous 
ocean  depths.  The  only  terrestrial  vertebrata  are 
two  lizards,  one  of  which  constitutes  a  peculiar 
genus.  There  are  24  aquatic  birds,  five  of  which  are 
peculiar ;  four  birds  of  prey,  two  of  which  are  pecu- 
liar; and  1 6  land-birds,  all  of  which  are  peculiar. 
Moreover,  these  16  land-birds  constitute  no  less 
than  10  peculiar  genera,  and  even  one  peculiar 
family  of  five  genera.  This  is  an  amount  of 
peculiarity  far  exceeding  that  of  any  other  islands, 
and,  of  course,  corresponds  with  the  great  isolation  of 
this  archipelago.  The  only  other  animals  which  have 
here  been  carefully  studied  are  the  land-shells,  and 
these  tell  the  same  story  as  the  birds.  For  there  are 


Geographical  Distribution.  235 

no  less  than  400  species  which  are  all,  without  any 
exception,  peculiar ;  while  about  three-quarters  of 
them  go  to  constitute  peculiar  genera.  Again,  of  the 
plants,  620  species  are  believed  to  be  endemic  ;  and 
of  these  377  are  peculiar,  yielding  no  less  than  39 
peculiar  genera. 

Prejudice  apart,  I  think  we  must  all  now  agree  that 
it  is  needless  to  continue  further  this  line  of  proof.  I 
have  chosen  the  smallest  and  most  isolated  islands 
for  the  purposes  of  our  present  argument,  first 
because  these  furnish  the  most  crucial  kind  of 
test,  and  next  because  they  best  admit  of  being  dealt 
with  in  a  short  space.  But,  if  necessary,  a  vast 
amount  of  additional  material  could  be  furnished, 
not  only  from  other  small  oceanic  islands,  but  still 
more  from  the  largest  islands  of  the  world,  such  as 
Australia  and  New  Zealand.  However,  after  the 
detailed  inventories  which  have  now  been  given 
in  the  case  of  some  of  the  smaller  islands  most 
remote  from  mainlands,  we  may  well  be  prepared  to 
accept  it  as  a  general  law,  that  wherever  there  is 
evidence  of  land-areas  having  been  for  a  long  time 
separated  from  other  land-areas,  there  we  meet  with 
a  more  or  less  extraordinary  profusion  of  unique 
species,  often  running  up  into  unique  genera.  And, 
in  point  of  fact,  so  far  as  naturalists  have  hitherto 
been  able  to  ascertain,  there  is  no  exception  to  this 
general  law  in  any  region  of  the  globe.  Moreover, 
there  is  everywhere  a  constant  correlation  between 
the  degree  of  this  peculiarity  on  the  part  of  the  fauna 
and  flora,  and  the  time  during  which  they  have  been 
isolated.  Thus,  for  instance,  among  the  islands  which 


236          Darwin,  and  after  Darwin. 


I  have  called  into  evidence,  those  that  are  at  once 
the  most  isolated  and  give  independent  proofs  of  the 
highest  antiquity,  are  the  Galapagos  Islands,  the  Sand- 
wich Islands,  and  St.  Helena.  Now,  if  we  apply  the 
method  of  tabular  analysis  to  these  three  cases,  we 
obtain  the  following  most  astonishing  results.  For 
the  sake  of  simplicity  I  will  omit  the  enumeration  of 
peculiar  genera,  and  confine  attention  to  peculiar 
species.  Moreover,  I  will  consider  only  terrestrial 
animals  ;  for,  as  we  have  already  seen,  aquatic  animals 
are  so  much  more  likely  to  reach  oceanic  islands  that 
they  do  not  furnish  nearly  so  fair  a  test  of  the  evolu- 
tionary hypothesis. 

PECULIAR  SPECIES. 


Sandwich  . 
Galapagos 
St.  Helena 

Shells. 

Insects. 

Reptiles. 

Birds. 

Mammals. 

400 
15 

20 

? 

35 
128 

2 
10 
0 

16 

30 

0 
0 
0 

Totals   . 

435 

163 

12 

47 

0 

NON-PECULIAR  SPECIES. 


Sandwich  . 

Shells. 

Insects. 

Reptiles. 

Birds. 

Mammals. 

0 

! 

o 

0 

0 

Galapagos 
St.  Helena 

? 

0 

? 
? 

0 
0 

I 

0 

0 
0 

Totals    . 

0 

? 

o 

I 

0 

From  this  synopsis  we  perceive  that  out  of  a  total 
of  658  species  of  terrestrial  animals  known  to  inhabit 


Geographical  Distribution.  237 

these  three  oceanic  territories,  all  are  peculiar,  with 
the  exception  of  a  single  land-bird  which  is  found  in 
the  Galapagos  Islands.  This  is  the  rice-bird,  so  very 
abundant  on  the  American  continent  that  its  repre- 
sentatives must  not  unfrequently  become  the  invo- 
luntary colonists  of  the  Archipelago.  There  are, 
however,  a  few  species  of  non-peculiar  insects  in- 
habiting the  Sandwich  and  Galapagos  Islands,  the 
exact  number  of  which  is  doubtful,  and  on  this 
account  are  not  here  quoted.  But  at  most  they 
would  be  represented  by  units,  and  therefore  do  not 
affect  the  general  result.  Lastly,  the  remarkable 
fact  will  be  noted,  that  there  is  no  single  represen- 
tative of  the  mammalian  class  in  any  of  these  islands. 
If  we  turn  next  to  consider  the  case  of  plants,  we 
obtain  the  following  result  : — 

Peculiar  Non-peculiar 
Species.  Species. 

Sandwich 377  243 

Galapagos 174  158 

St.  Helena 50  26 

Totals 601  437 

So  that  by  adding  together  peculiar  species  both 
of  land-animals  and  plants,  we  find  that  on  these 
three  limited  areas  alone  there  are  1258  forms  of  life 
which  occur  nowhere  else  upon  the  globe — not  to 
speak  of  the  peculiar  aquatic  species,  nor  of  the 
presumably  large  number  of  peculiar  species  of  all 
kinds  not  hitherto  discovered  in  these  imperfectly 
explored  regions. 

Now  let  us  compare  these  facts  with  those  which 
are  presented  by  the  faunas  and  floras  of  islands  less 


238          Darwin,  and  after  Darwin. 

remote  from  continents,  and  known  from  independent 
geological  evidence  to  be  of  comparatively  recent 
origin — that  is,  to  have  been  separated  from  their 
adjacent  mainlands  in  comparatively  recent  times, 
and  therefore  as  islands  to  be  comparatively  young. 
The  British  Isles  furnish  as  good  an  instance  as  could 
be  chosen,  for  they  together  comprise  over  1000 
islands  of  various  sizes,  which  are  nowhere  separated 
from  one  another  by  deep  seas,  and  in  the  opinion  of 
geologists  were  all  continuous  with  the  European 
continent  since  the  glacial  period. 


BRITISH  ISLES. 

NON-PECULIAR  SPECIES. 


Plants. 

Land 
Shells. 

Insects. 

Reptiles 
and 
Amphibia. 

Lund 
Birds. 

Land 

Mammals. 

1462 

83 

J2.55i 

13 

130 

40 

PECULIAR   SPECIES. 


Plants. 

Shells.        Insects. 

j 

Reptiles 
and 
Amphibia. 

Land 
Birds. 

Land 
Mammals. 

46 

4         !       M9 

0 

i 

0 

Total  Peculiar  Plants    . 
Total  Peculiar  Animals 


46 
154 


Grand  Total 200 

I  have  drawn   up   this   table  in  the  most  liberal 
manner  possible,  including  as  peculiar  species  forms 


Geographical  Distribution.  239 

which  many  naturalists  regard  as  merely  local  varie- 
ties. But,  even  as  thus  interpreted,  how  wonderful  is 
the  contrast  between  the  1000  islands  of  Great  Britain 
and  the  single  volcanic  rock  of  St.  Helena,  where 
almost  all  the  animals  and  about  half  the  plants  are 
peculiar,  instead  of  about  ¥V  °f tne  animals,  and  -fa  of 
the  plants.  Of  course,  if  no  peculiar  species  of  any 
kind  had  occurred  in  the  British  Isles,  advocates  of 
special  creation  might  have  argued  that  it  was,  so  to 
speak,  needless  for  the  Divinity  to  have  added  any 
new  species  to  those  European  forms  which  fully 
populated  the  islands  at  the  time  when  they  were 
separated  from  the  continent.  But;  as  the  matter 
stands,  advocates  of  special  creation  must  face  the 
fact  that  a  certain  small  number  of  new  and  peculiar 
species  have  been  formed  on  the  British  Isles ;  and, 
therefore,  that  creative  activity  has  not  been  wholly 
suspended  in  their  case.  Why,  then,  has  it  been  so 
meagre  in  this  case  of  a  thousand  islands,  when  it  has 
proved  so  profuse  in  the  case  of  all  single  islands 
more  remote  from  mainlands,  and  presenting  a  higher 
antiquity  ?  Or  why  should  the  Divinity  have  thus 
appeared  so  uniformly  to  consult  these  merely  acci- 
dental circumstances  of  space  and  time  in  the  de- 
positing of  his  unique  specific  types  ?  Do  not  such 
facts  rather  speak  with  irresistible  force  in  favour  of  the 
view,  that  while  all  ancient  and  solitary  islands  have 
had  time  enough,  and  separation  enough,  to  admit  of 
distinct  histories  of  evolution  having  been  written  in 
their  living  inhabitants,  no  one  of  the  thousand  islands 
of  Great  Britain  has  had  either  time  enough,  or  separa- 
tion enough,  to  have  admitted  of  more  than  some  of  the 
first  pages  of  such  a  history  having  been  commenced  ? 


240          Darwin,  and  after  Darwin. 

But  this  allusion  to  Great  Britain  introduces  us  to 
another  point.  It  will  have  been  observed  that, 
unlike  oceanic  islands  remote  from  mainlands,  Great 
Britain  is  well  furnished  both  with  reptiles  (including 
amphibia)  and  mammals.  For  there  is  no  instance  of 
any  oceanic  island  situated  at  more  than  300  miles 
from  a  continent  where  any  single  species  of  the 
whole  class  of  mammals  is  to  be  found,  excepting 
species  of  the  only  order  which  is  able  to  fly — namely, 
the  bats.  And  the  same  has  to  be  said  of  frogs,  toads, 
and  newts,  whose  spawn  is  quickly  killed  by  contact 
with  sea-water,  and  therefore  could  never  have  reached 
remote  islands  in  a  living  state.  Hence,  on  evolu- 
tionary principles,  it  is  quite  intelligible  why  oceanic 
islands  should  not  present  any  species  of  mammals  or 
batrachians — peculiar  or  otherwise,  -  save  such  species 
of  mammals  as  are  able  to  fly.  But  on  the  theory 
of  special  creation  we  can  assign  no  reason  why, 
notwithstanding  the  extraordinary  profusion  of  unique 
types  of  other  kinds  which  we  have  seen  to  occur  on 
oceanic  islands,  the  Deity  should  have  made  this 
curious  exception  to  the  detriment  of  all  frogs,  toads, 
newts,  and  mammals,  save  only  such  as  are  able  to  fly. 
Or,  if  any  one  should  go  so  far  to  save  a  desperate 
hypothesis  as  to  maintain  that  there  must  have  been 
some  hidden  reason  why  batrachians  and  quadrupeds 
were  not  specially  created  on  oceanic  islands,  I  may 
mention  another  small — but  in  this  relation  a  most 
significant — fact.  This  is  that  on  some  of  these 
islands  there  occur  certain  peculiar  species  of  plants, 
the  seeds  of  which  are  provided  with  numerous  tiny 
hooks,  obviously  and  beautifully  adapted — like  those 
on  the  seeds  of  allied  plants  elsewhere — to  catch  the 


Geographical  Distribution.  241 

wool  or  hair  of  moving  quadrupeds,  and  so  to  further 
their  own  dissemination.  But,  as  we  have  just  seen, 
there  are  no  quadrupeds  in  the  islands  to  meet 
these  beautiful  adaptations  on  the  part  of  the  plants  ; 
so  that  special  creationists  must  resort  to  the  almost 
impious  supposition  that  in  these  cases  the  Deity  has 
only  carried  out  half  his  plan,  in  that  while  he  made 
an  elaborate  provision  for  these  uniquely  created 
species  of  plants,  which  depended  for  its  efficiency  on 
the  presence  of  quadrupeds,  he  nevertheless  neglected 
to  place  any  quadrupeds  on  the  islands  where  he  had 
placed  the  plants.  Such  one-sided  attempts  at  adap- 
tation surely  resolve  the  thesis  of  special  creation  to  a 
rediictio  ad  absurdum  ;  and  hence  the  only  reasonable 
interpretation  of  them  is,  that  while  the  seeds  of  allied 
or  ancestral  plants  were  able  to  float  to  the  islands,  no 
quadrupeds  were  ever  able  over  so  great  a  distance  to 
swim. 

Although  much  more  evidence  might  still  be  given 
under  the  head  of  geographical  distribution,  I  must 
now  close  with  a  brief  summary  of  the  main  points 
that  have  been  adduced. 

After  certain  preliminary  considerations,  I  began 
by  noticing  that  the  theory  of  evolution  has  a  much 
more  intelligible  account  to  give  than  has  its  rival  of 
the  facts  of  discontinuous  distribution — the  Alpine 
flora,  for  instance,  being  allied  to  the  Arctic,  not 
because  the  same  species  were  separately  created  in 
both  places,  but  because  during  the  glacial  period 
these  species  extended  all  over  Europe,  and  were 
left  behind  on  the  Alps  as  the  Arctic  flora  receded 
northwards — which  was  sufficiently  long  ago  to  ex- 

*  R 


242  Darwin,  and  after  Darwin. 

plain   why  some  of  the  Alpine  species  are   unique, 
though  closely  allied  to  Arctic  forms. 

Next  we  saw  that,  although  living  things  are  always 
adapted  to  the  climates  under  which  they  live  (since 
otherwise  they  could  not  live  there  at  all),  it  is  equally 
true  that,  as  a  rule,  besides  the  area  on  which  they  do 
live,  there  are  many  other  areas  in  different  parts  of 
the  globe  where  they  might  have  lived  equally  well. 
Consequently  we  must  conclude  that,  if  all  species 
were  separately  created,  many  species  were  severally 
created  on  only  one  among  a  number  of  areas  where 
they  might  equally  well  have  thrived.  Now,  although 
this  conclusion  in  itself  may  not  seem  opposed  to  the 
theory  of  special  creation,  a  most  serious  difficulty  is 
raised  when  it  is  taken  in  connexion  with  another  fact 
of  an  equally  general  kind.  This  is,  that  on  every 
biological  region  we  encounter  chains  of  allied  species 
constituting  allied  genera,  families,  and  so  on ;  while 
we  scarcely  ever  meet  with  allied  species  in  different 
biological  regions,  notwithstanding  that  their  climates 
may  be  similar,  and,  consequently,  just  as  well  suited 
to  maintain  some  of  the  allied  species.  Hence  we 
must  further  conclude,  if  all  species  were  separately 
created,  that  in  the  work  of  creation  some  unac- 
countable regard  was  paid  to  making  areas  of  dis- 
tribution correspond  to  degrees  of  structural  affinity. 
A  great  many  species  of  the  rat  genus  were  created 
in  the  Old  World,  and  a  great  many  species  of 
another,  though  allied,  genus  were  created  in  the 
New  World :  yet  no  reason  can  be  assigned  why  no 
one  species  of  the  Old  World  series  should  not  just 
as  well  have  been  deposited  in  the  New  World,  and 
•vice  versa.  On  the  other  hand,  the  theory  of  evolution 


Geographical  Distribution.  243 

may  claim  as  direct  evidence  in  its  support  all  the 
innumerable  cases  such  as  these — cases,  indeed,  so 
innumerable  that,  as  Mr.  Wallace  remarks,  it  may 
be  taken  as  a  law  of  nature  that  "  every  species  has 
come  into  existence  coincident  both  in  space  and 
time  with  a  pre-existing  and  closely  allied  species." 
A  general  law  which,  while  in  itself  most  strongly 
suggestive  of  evolution,  is  surely  impossible  to 
reconcile  with  any  reasonable  theory  of  special 
creation.  Furthermore,  this  law  extends  backwards 
through  all  geological  time,  with  the  result  that  the 
extinct  species,  which  now  occur  only  as  fossils  on 
any  given  geological  area,  resemble  the  species  still 
living  upon  that  area,  as  we  should  expect  that  they 
must,  if  the  former  were  the  natural  progenitors  of 
the  latter.  On  the  other  hand,  if  they  were  not  the 
natural  progenitors,  but  all  the  species,  both  living 
and  extinct,  were  the  supernatural  and  therefore  in- 
dependent creations  which  the  rival  theory  would 
suppose,  then  no  reason  can  be  given  why  the  extinct 
species  should  thus  resemble  the  living — any  more 
than  why  the  living  species  should  resemble  one 
another.  For,  as  we  have  seen,  there  are  almost 
always  many  other  habitats  on  other  parts  of  the 
globe,  where  any  members  of  any  given  group  of 
species  might  equally  well  have  been  deposited  ; 
and  this,  of  course,  applies  to  geological  no  less  than 
to  historical  time.  Yet  throughout  all  time  we  meet 
with  this  most  suggestive  correlation  between  con- 
tinuity of  a  geographical  area  and  structural  affinity 
between  the  forms  of  life  which  have  lived,  or  are  still 
living,  upon  that  area. 

Similarly,  we  find  the  further,  and  no  less  suggestive, 
R  2 


244          Darwin,  and  after  Darwin. 

correlation  between  the  birth  of  new  species  and  the 
immediate  pre-existence  of  closely  allied  species  on 
the  same  area — or,  at  most,  on  closely  contiguous  areas. 

Where  a  continuous  area  has  long  been  circum- 
scribed by  barriers  of  any  kind,  which  prevent  the 
animals  from  wandering  beyond  it,  then  we  find  that 
all  the  species,  both  extinct  and  living,  constitute 
more  or  less  a  world  of  their  own  ;  while,  on  the 
other  hand,  where  the  animals  are  free  to  migrate 
from  one  area  to  another,  the  course  of  their  migra- 
tions is  marked  by  the  origination  of  new  species 
springing  up  en  route,  and  serving  to  connect  the 
older,  or  metropolitan,  forms  with  the  younger,  or 
colonising,  forms  in  the  way  of  a  graduated  series. 
This  principle,  however,  admits  of  being  traced  only 
in  certain  cases  of  species  belonging  to  the  same 
genus,  of  genera  belonging  to  the  same  family,  or, 
at  most,  of  families  belonging  to  the  same  order. 
In  other  words,  the  more  general  the  structural 
affinity,  the  more  general  is  the  geographical  ex- 
tension— as  we  should  expect  to  be  the  case  on  the 
theory  of  descent  with  branching  modifications,  seeing 
that  the  larger,  the  older,  and  the  more  diverse  the 
group  of  organisms  compared,  the  greater  must  be 
their  chances  of  dispersal. 

These  general  considerations  led  us  to  contemplate 
more  in  detail  the  correlation  between  structural 
affinity  and  barriers  to  free  migration.  Such  barriers, 
of  course,  differ  in  the  cases  of  different  organisms. 
Marine  organisms  are  stopped  by  land,  unsuitable 
temperature,  or  unsuitable  depths ;  fresh-water  or- 
ganisms by  sea  and  by  mountain-chains ;  terrestrial 
organisms  chiefly  by  water.  Now  it  is  a  matter  of 


Geographical  Distribution.  245 

fact  which  admits  of  no  dispute,  that  in  each  of  these 
cases  we  meet  with  a  direct  correlation  between  the 
kind  of  barrier  and  the  kind  of  organisms  whose 
structural  affinities  are  affected  thereby.  Where  we 
have  to  do  with  marine  organisms,  barriers  such  as 
the  Isthmus  of  Panama  and  the  varying  depth  of  the 
Western  Pacific  determine  three  very  distinct  faunas, 
ranging  north  and  south  in  closely  parallel  lines,  and 
under  corresponding  climates.  Where  we  have  to  do 
with  fresh-water  organisms,  we  find  that  a  mountain- 
chain  only  a  few  miles  wide  has  more  influence  in 
determining  differences  of  organic  type  on  either  side 
of  it  than  is  exercised  by  even  thousands  of  miles  of 
a  continuous  land-area,  if  this  be  uninterrupted  by 
any  mountains  high  enough  to  prevent  water-fowl, 
whirlwinds,  &c.,  from  dispersing  the  ova.  Again, 
where  we  have  to  do  with  terrestrial  organisms,  the 
most  effectual  barriers  are  wide  reaches  of  ocean ; 
and,  accordingly,  we  find  that  these  exercise  an 
enormous  influence  on  the  modification  of  terrestrial 
types.  Moreover,  we  find  that  the  more  terrestrial 
an  organism,  or  the  greater  the  difficulty  it  has  in 
traversing  a  wide  reach  of  ocean,  the  greater  is  the 
modifying  influence  of  such  a  barrier  upon  that  type. 
In  oceanic  islands,  for  example,  many  of  the  plants 
and  aquatic  birds  usually  belong  to  the  same  species 
as  those  which  occur  on  the  nearest  mainlands,  and 
where  there  are  any  specific  differences,  these  but 
rarely  run  up  to  generic  differences.  But  the  land- 
birds,  insects,  and  reptiles  which  are  found  on  such 
islands  are  nearly  always  specifically,  and  very  often 
generically,  distinct  from  those  on  the  nearest  main- 
land—although invariably  allied  with  sufficient  close- 


246  Darwin,  and  after  Darwin. 

ness  to  leave  no  manner  of  doubt  as  to  their  affinities 
with  the  fauna  of  that  mainland.  Lastly,  no  am- 
phibians and  no  mammals  (except  bats)  are  ever 
found  on  any  oceanic  islands.  Yet,  as  we  have  seen, 
on  the  theory  of  special  creation,  these  islands  must 
all  be  taken  to  have  been  the  theatres  of  the  most 
extraordinary  creative  activity,  so  that  on  only  three 
of  them  we  found  no  less  than  1258  unique  species, 
whereof  657  were  unique  species  of  land  animals,  to 
be  set  against  one  single  species  known  to  occur  else- 
where. Nevertheless,  notwithstanding  this  prodigious 
expenditure  of  creative  energy  in  the  case  of  land- 
birds,  land-shells,  insects,  and  reptiles,  no  single  new 
amphibian,  or  no  single  new  mammal,  has  been 
created  on  any  single  oceanic  island,  if  we  except 
the  only  kind  of  mammal  that  is  able  to  fly,  and 
the  ancestors  of  which,  like  those  of  the  land-birds 
and  insects,  might  therefore  have  reached  the  "islands 
ages  ago.  Moreover,  with  regard  to  mammals, 
even  in  cases  where  allied  forms  occur  on  either 
side  of  a  sea- channel,  it  is  found  to  be  a  general  rule 
that  if  the  channel  is  shallow,  the  species  on  either 
side  of  it  are  much  more  closely  related  than  if  it  be 
deep — and  this  irrespective  of  its  width.  Therefore 
we  can  only  conclude,  in  the  words  of  Darwin — "  As 
the  amount  of  modification  which  animals  of  all  kinds 
undergo  partly  depends  on  lapse  of  time,  and  as  the 
islands  which  are  separated  from  each  other  or  from 
the  mainland  by  shallow  channels  are  more  likely  to 
have  been  continuously  united  within  a  recent  period 
than  islands  separated  by  deeper  channels,  we  can 
understand  how  it  is  that  a  relation  exists  between 
the  depth  of  the  sea  separating  two  mammalian 


Geographical  Distribution.  247 

faunas,  and  the  degree  of  their  affinity— a  relation 
which  is  quite  inexplicable  on  the  theory  of  inde- 
pendent acts  of  creation." 

Looking  to  all  these  general  principles  of  geo- 
graphical distribution,  and  remembering  the  sundry 
points  of  smaller  detail  relating  to  oceanic  islands 
which  I  will  not  wait  to  recapitulate,  to  my  mind  it 
seems  that  there  is  no  escape  from  the  following 
conclusion,  with  which  I  will  bring  my  brief  epitome 
of  the  evidence  to  a  close.  The  conclusion  to  which, 
I  submit,  all  the  evidence  leads  is,  that  if  the  doctrine 
of  special  creation  is  taken  to  be  true,  then  it  must 
be  further  taken  that  the  one  and  only  principle 
which  has  been  consistently  followed  in  the  geo- 
graphical deposition  of  species,  is  that  of  so  de- 
positing them  as  to  make  it  everywhere  appear  that 
they  were  not  thus  deposited  at  all,  but  came  into 
existence  where  they  now  occur  by  way  of  genetic 
descent  with  perpetual  migration  and  correlative 
modification.  On  no  other  principle,  so  far  as  I 
can  see,  would  it  be  possible  to  account  for  the  fact 
that  "every  species  has  come  into  existence  coincident 
both  in  space  and  time  with  a  pre-existing  and  closely 
allied  species,"  together  with  the  carefully  graduated 
regard  to  physical  barriers  which  the  Creator  must 
have  displayed  while  depositing  his  newly  formed 
species  on  either  sides  of  them — everywhere  making 
degrees  of  structural  affinity  correspond  to  degrees  of 
geographical  continuity,  and  degrees  of  structural  differ- 
ence correspond  to  degrees  of  geographical  separation, 
whether  by  mountain-chains  in  the  case  of  fresh-water 
faunas,  by  land  and  by  deep  sea  in  the  case  of  marine 


248          Darwin,  and  after  Darwin. 

faunas,  or  by  reaches  of  ocean  in  the  case  of  terrestrial 
faunas— stocking  oceanic  islands  with  an  enormous 
profusion  of  peculiar  species  all  allied  to  those  on  the 
nearest  mainlands,yet  everywhere  avoiding  the  creation 
upon  them  of  any  amphibian  or  mammal,  except  an 
occasional  bat.  We  are  familiar  with  the  doctrine 
that  God  is  a  God  who  hideth  himself;  here,  however, 
it  seems  to  me,  we  should  have  but  a  thinly-veiled 
insinuation,  not  merely  that  in  his  works  he  is 
hidden,  but  that  in  these  works  he  is  untrue.  Than 
which  I  cannot  conceive  a  stronger  condemnation  of 
the  theory  which  it  has  been  my  object  fairly  to 
represent  and  dispassionately  to  criticise. 


SECTION  II 

SELECTION 


CHAPTER    VII. 

THE  THEORY  OF  NATURAL  SELECTION. 

THUS  far  we  have  been  considering  the  main 
evidences  of  organic  evolution  considered  as  a  fact. 
We  now  enter  a  new  field,  namely,  the  evidences 
which  thus  far  have  been  brought  to  light  touching 
the  causes  of  organic  evolution  considered  as  a  pro- 
cess. 

As  was  pointed  out  in  the  opening  chapter,  this  is 
obviously  the  methodical  course  to  follow :  we  must 
have  some  reasonable  assurance  that  a  fact  is  a  fact 
before  we  endeavour  to  explain  it.  Nevertheless,  it 
is  not  necessary  that  we  should  actually  demonstrate 
a  fact  to  be  a  fact  before  we  endeavour  to  explain  it. 
Even  if  we  have  but  a  reasonable  presumption  as  to 
its  probability,  we  may  find  it  well  worth  while  to  con- 
sider its  explanation;  for  by  so  doing  we  may  obtain 
additional  evidence  of  the  fact  itself.  And  this  because, 
if  it  really  is  a  fact,  and  if  we  hit  upon  the  right 
explanation  of  it,  by  proving  the  explanation  probable, 
we  may  thereby  greatly  increase  our  evidence  of  the  fact. 
In  the  very  case  before  us,  for  example,  the  evidence 
of  evolution  as  a  fact  has  from  the  first  been  largely 
derived  from  testing  Darwin's  theory  concerning  its 
method.  It  was  this  theoretical  explanation  of  its 


252          Darwin,  and  after  Darwin. 

method  which  first  set  him  seriously  to  enquire  into 
the  evidences  of  evolution  as  a  fact ;  and  ever  since  he 
published  his  results,  the  evidences  which  he  adduced 
in  favour  of  natural  selection  as  a  method  have  con- 
stituted some  of  the  strongest  reasons  which  scientific 
men  have  felt  for  accepting  evolution  as  a  fact.  Of 
course  the  evidence  in  favour  of  this  fact  has  gone  on 
steadily  growing,  quite  independently  of  the  assistance 
which  was  thus  so  largely  lent  to  it  by  the  distinct- 
ively Darwinian  theory  of  its  method  ;  and,  indeed,  so 
much  has  this  been  the  case,  that  in  the  present  treatise 
we  have  been  able  to  consider  such  direct  evidence  of 
the  fact  itself,  without  any  reference  at  all  to  the  indirect 
or  accessory  evidence  which  is  derived  from  that  of 
natural  selection  as  a  method.  From  which  it  follows 
that  in  most  of  what  I  am  about  to  say  in  subsequent 
chapters  on  the  evidences  of  natural  selection  as  a 
method,  there  will  be  furnished  a  large  addition  to  the 
evidences  which  have  already  been  detailed  of  evolution 
as  a  fact.  But,  as  a  matter  of  systematic  treatment,  I 
have  thought  it  desirable  to  keep  these  two  branches  of 
our  subject  separate.  Which  means  that  I  have  made 
the  evidences  of  evolution  as  a  fact  to  stand  indepen- 
dently on  their  own  feet — feet  which  in  my  opinion  are 
amply  strong  enough  to  bear  any  weight  of  adverse 
criticism  that  can  be  placed  upon  them. 

Our  position,  then,  is  this.  On  the  foundation  of 
the  previous  chapters,  I  will  henceforth  assume  that 
we  all  accept  organic  evolution  as  a  fact,  without 
requiring  any  of  the  accessory  evidence  which  is  gained 
by  independent  proof  of  natural  selection  as  a  method. 
But  in  making  this  assumption — namely,  that  we  are 
all  now  firmly  persuaded  of  the  fact  of  evolution — I  do 


The   Theory  of  Natural  Selection.     253 

not  imagine  that  such  is  really  the  case.  I  make  the 
assumption  for  the  purposes  of  systematic  exposition, 
and  in  order  that  different  parts  of  the  subject  may  be 
kept  distinct.  I  confess  it  does  appear  to  me  remark- 
able that  there  should  still  be  a  doubt  in  any  educated 
mind  touching  the  general  fact  of  evolution  ;  while  it 
becomes  to  me  unaccountable  that  such  should  be 
the  case  with  a  few  still  living  men  of  science,  who 
cannot  be  accused  of  being  ignorant  of  the  evidences 
which  have  now  been  accumulated.  But  in  whatever 
measure  we  may  severally  have  been  convinced — or  re- 
mained unconvinced — on  this  matter,  for  the  purposes 
of  exposition  I  must  hereafter  assume  that  we  are  all 
agreed  to  the  extent  of  regarding  the  process  of 
evolution  as,  at  least,  sufficiently  probable  to  justify 
enquiry  touching  its  causes  on  supposition  of  its 
truth. 

Now,  the  causes  of  evolution  have  been  set  forth  in 
a  variety  of  different  hypotheses,  only  the  chief  of 
which  need  be  mentioned  here.  Historically  speaking 
the  first  of  these  was  that  which  was  put  forward  by 
Erasmus  Darwin,  Lamarck,  and  Herbert  Spencer. 
It  consists  in  putting  together  the  following  facts 
and  inferences. 

We  know  that,  in  the  lifetime  of  the  individual, 
increased  use  of  structures  leads  to  an  increase 
of  their  functional  efficiency;  while,  on  the  other 
hand,  disuse  leads  to  atrophy.  The  arms  of  a  black- 
smith, and  the  legs  of  a  mountaineer,  are  familiar 
illustrations  of  the  first  principle :  our  hospital  wards 
are  full  of  illustrations  of  the  second.  Again,  we  know 
that  the  characters  of  parents  are  transmitted  to  their 
progeny  by  means  of  heredity.  Now  the  hypothesis 


254          Darwin,  and  after  Darwin. 

in  question  consists  in  supposing  that  if  any  particular 
organs  in  a  species  are  habitually  used  for  performing 
any  particular  action,  they  must  undergo  a  structural 
improvement  which  would  more  and  more  adapt  them 
to  the  performance  of  that  action  ;  for  in  each  gene- 
ration constant  use  would  better  and  better  adapt  the 
structures  to  the  discharge  of  their  functions,  and  they 
would  then  be  bequeathed  to  the  next  generation  in 
this  their  improved  form  by  heredity.  So  that,  for  in- 
stance, if  there  had  been  a  thousand  generations  of 
blacksmiths,  we  might  expect  the  sons  of  the  last  of 
them  to  inherit  unusually  strong  arms,  even  if  these 
young  men  had  themselves  taken  to  some  other  trade 
not  requiring  any  special  use  of  their  arms.  Similarly, 
if  there  had  been  a  thousand  generations  of  men 
who  used  their  arms  but  slightly,  we  should  expect 
their  descendants  to  show  but  a  puny  development  of 
the  upper  extremities.  Now  let  us  apply  all  this  to  the 
animal  kingdom  in  general.  The  giraffe,  for  instance, 
is  a  ruminant  whose  entire  frame  has  been  adapted  to 
support  an  enormously  long  neck,  which  is  of  use  to 
the  animal  in  reaching  the  foliage  of  trees.  The  an- 
cestors of  the  giraffe,  having  had  ordinary  necks,  were 
supposed  by  Lamarck  to  have  gradually  increased  the 
length  of  them,  through  many  successive  generations, 
by  constantly  stretching  to  reach  high  foliage  ;  and  he 
further  supposed  that,  when  the  neck  became  so  long 
as  to  require  for  its  support  special  changes  in  the 
general  form  of  the  animal  as  a  whole,  these  special 
changes  would  have  brought  about  the  dwindling  of 
other  parts  from  which  so  much  activity  was  no  longer 
required — the  general  result  being  that  the  whole  or- 
ganization of  the  animal  became  more  and  more 


The   Theory  of  Natural  Selection.     255 

adapted  to  browsing  on  high  foliage.  And  so  in  the 
cases  of  other  animals,  Lamarck  believed  that  the 
adaptation  of  their  forms  to  their  habits  could  be  ex- 
plained by  this  simple  hypothesis  that  the  habits 
created  the  forms,  through  the  effects  of  use  and  dis- 
use, coupled  with  heredity. 

Such  is  what  is  ordinarily  known  as  Lamarck's 
theory  of  evolution.  We  may  as  well  remember, 
however,  that  it  really  constitutes  only  one  part  of  his 
theory  ;  for  besides  this  hypothesis  of  the  cumulative 
inheritance  of  functionally-produced  modifications — to 
which  we  may  add  the  inherited  effects  of  any  direct 
action  exercised  by  surrounding  conditions  of  life, — 
Lamarck  believed  in  some  transcendental  principle 
tending  to  produce  gradual  improvement  in  pre-de- 
termined  lines  of  advance.  Therefore  it  would  really 
be  more  correct  to  designate  the  former  hypothesis  by 
the  name  either  of  Erasmus  Darwin,  or,  still  better,  of 
Herbert  Spencer.  Nevertheless,  in  order  to  avoid  con- 
fusion, I  will  follow  established  custom,  and  subse- 
quently speak  of  this  hypothesis  as  the  Lamarckian 
hypothesis — understanding,  however,  that  in  employ- 
ing this  designation  I  am  not  referring  to  any  part 
or  factor  of  Lamarck's  general  theory  of  evolution 
other  than  the  one  which  has  just  been  described — 
namely,  the  hypothesis  of  the  cumulative  transmission 
of  functionally-produced,  or  otherwise  "acquired," 
modifications. 

This,  then,  was  the  earliest  hypothesis  touching  the 
causes  of  organic  evolution.  But  we  may  at  once 
perceive  that  it  is  insufficient  to  explain  all  that  stands 
to  be  explained.  In  the  first  place,  it  refers  in  chief 
part  only  to  the  higher  animals,  which  are  actuated  to 


256          Darwin,  and  after  Darwin. 

effort  by  intelligence.  Its  explanatory  power  in  the 
case  of  most  invertebrata — as  well  as  in  that  of  all  plants 
— is  extremely  limited,  inasmuch  rs  these  organisms 
can  never  be  moved  to  a  greater  or  less  use  of  their 
several  parts  by  any  discriminating  volition,  such  as 
that  which  leads  to  the  continued  straining  of  a 
giraffe's  neck  for  the  purpose  of  reaching  foliage.  In 
the  second  place,  even  among  the  higher  animals  there 
are  numberless  tissues  and  organs  which  unques- 
tionably present  a  high  degree  of  adaptive  evolution, 
but  which  nevertheless  cannot  be  supposed  to  have 
fallen  within  the  influence  of  Lamarckian  principles. 
Of  such  are  the  shells  of  Crustacea,  tortoises,  &c., 
which  although  undoubtedly  of  great  use  to  the 
animals  presenting  them,  cannot  ever  have  been  used 
in  the  sense  required  by  Lamarck's  hypothesis,  i.  e. 
actively  exercised,  so  as  to  increase  a  flow  of  nutrition 
to  the  part.  Lastly,  in  the  third  place,  the  validity  of 
Lamarck's  hypothesis  in  any  case  whatsoever  has  of 
late  years  become  a  matter  of  serious  question,  as  will 
be  fully  shown  and  discussed  in  the  next  volume. 
Meanwhile  it  is  enough  to  observe  that,  on  account  of 
all  these  reasons,  the  theory  of  Lamarck,  even  if  it  be 
supposed  to  present  any  truth  at  all,  is  clearly  in- 
sufficient as  a  full  or  complete  theory  of  organic 
evolution. 

In  historical  order  the  next  theory  that  was  arrived 
at  was  the  theory  of  natural  selection,  simultaneously 
published  by  Darwin  and  Wallace  on  July  ist,  1858. 

If  we  may  estimate  the  importance  of  an  idea  by 
the  change  of  thought  which  it  effects,  this  idea  of 
natural  selection  is  unquestionably  the  most  important 


The   Theory  of  Natural  Selection.     257 

idea  that  has  ever  been  conceived  by  the  mind  of  man. 
Yet  the  wonder  is  that  it  should  not  have  been 
hit  upon  long  before.  Or  rather,  I  should  say,  the 
wonder  is  that  its  immense  and  immeasurable  impor- 
tance should  not  have  been  previously  recognised. 
For,  since  the  publication  of  this  idea  by  Darwin  and 
Wallace,  it  has  been  found  that  its  main  features  had 
already  occurred  to  at  least  two  other  minds — namely, 
Dr.  Wells  in  1813,  and  Mr.  Patrick  Matthew  in  1831. 
But  neither  of  these  writers  perceived  that  in  the  few 
scattered  sentences  which  they  had  written  upon  the 
subject  they  had  struck  the  key-note  of  organic  nature, 
and  resolved  one  of  the  principal  chords  of  the  universe. 
Still  more  remarkable  is  the  fact  that  Mr.  Herbert 
Spencer — notwithstanding  his  gn.at  powers  of  abstract 
thought  and  his  great  devotion  of  those  powers  to  the 
theory  of  evolution,  when  as  yet  this  theory  was  scorned 
by  science — still  more  remarkable;  I  say,  is  the  fact  that 
Mr.  Herbert  Spencer  should  have  nrssed  what  now 
appears  so  obvious  an  idea.  But  most  remarkable  of 
all  is  the  fact  that  Dr.  Whewell,  with  all  his  stores  of 
information  on  the  history  of  the  inductive  sciences, 
and  with  all  his  acumen  on  the  matter  of  scientific 
method,  should  not  only  have  conceived  the  idea  of 
natural  selection,  but  expressly  stated  it  as  a  logically 
possible  explanation  of  the  origin  of  species,  and  yet 
have  so  stated  it  merely  for  the  purpose  of  dismissing 
it  with  contempt J.  This,  I  think,  is  most  remarkable, 
because  it  serves  to  prove  how  very  far  men's  minds  at 
that  time  must  have  been  from  entertaining,  as  in  any 
way  antecedently  probable,  the  doctrine  of  trans- 
mutation. In  order  to  show  this  I  will  here  quote  one 

1  For  quotations,  see  Note  A. 
*  S 


258          Darwin,  and  after  Darwin. 

passage  from  the  writings  of  Whewell,  and  another 
from  a  distinguished  French  naturalist  referred  to  by 
him. 

In  1846  Whewell  wrote: — 

Not  only  is  the  doctrine  of  the  transmutation  of  species  in 
itself  disproved  by  the  best  physiological  reasonings,  but  the 
additional  assumptions  which  are  requisite  to  enable  its  ad- 
vocates to  apply  it  to  the  explanation  of  the  geological  and 
other  phenomena  of  the  earth,  are  altogether  gratuitous  and 
fantastical  \ 

Then  he  quotes  with  approval  the  following 
opinion : — 

Against  this  hypothesis,  which,  up  to  the  present  time,  I  regard 
as  purely  gratuitous,  and  likely  to  turn  geologists  out  of  the 
sound  and  excellent  road  in  which  they  now  are,  I  willingly  raise 
my  voice,  with  the  most  absolute  conviction  of  being  in  the 
right 2. 

And,  after  displaying  the  proof  rendered  by  Lycll 
of  uniformitarianism  in  geology,  and  cordially  sub- 
scribing thereto,  Whewell  adds  : — 

We  are  led  by  our  reasonings  to  this  view,  that  the  present 
order  of  things  was  commenced  by  an  act  of  creative  power 
entirely  different  to  any  agency  which  has  been  exerted  since. 
None  of  the  influences  which  have  modified  the  present  races  of 
animals  and  plants  since  they  were  placed  in  their  habitations  on 
the  earth's  surface  can  have  had  any  efficacy  in  producing  them 
at  first.  We  are  necessarily  driven  to  assume,  as  the  beginning 
of  the  present  cycle  of  organic  nature,  an  event  not  included  in 
the  course  of  nature  3. 

So  much,  then,  for  the  state  of  the  most  enlightened 
and  representative  opinions  on  the  question  of  evolution 

1  Whewell,  Indications  of  the  Creator,  2nd  ed.,  1846. 
*  DC  Blainville,  Compte  Rendu,  1837. 
»  Whewell,  ibid.,  p.  162. 


The   Theory  of  Natural  Selection.      259 

before  the  publication  of  Darwin's  work  ;  and  so  much, 
likewise,  for  the  only  reasonable  suggestions  as  to 
the  causes  of  evolution  which  up  to  that  time  had 
been  put  forward,  even  by  those  few  individuals  who 
entertained  any  belief  in  evolution  as  a  fact.  It 
was  the  theory  of  natural  selection  that  changed  all 
this,  and  created  a  revolution  in  the  thought  of  our 
time,  the  magnitude  of  which  in  many  of  its  far-reaching 
consequences  we  are  not  even  yet  in  a  position  to 
appreciate ;  but  the  action  of  which  has  already 
wrought  a  transformation  in  general  philosophy,  as 
well  as  in  the  more  special  science  of  biology,  that 
is  without  a  parallel  in  the  history  of  mankind. 

Although  every  one  is  now  more  or  less  well 
acquainted  with  the  theory  of  natural  selection,  it  is 
necessary,  for  the  sake  of  completeness,  that  I  should 
state  the  theory ;  and  I  will  do  so  in  full  detail. 

It  is  a  matter  of  observable  fact  that  all  plants  and 
animals  are  perpetually  engaged  in  what  Darwin  calls 
a  "  struggle  for  existence."  That  is  to  say,  in  every 
generation  of  every  species  a  great  many  more  in- 
dividuals are  born  than  can  possibly  survive ;  so  that 
there  is  in  consequence  a  perpetual  battle  for  life  going 
on  among  all  the  constituent  individuals  of  any  given 
generation.  Now,  in  this  struggle  for  existence,  which 
individuals  will  be  victorious  and  live?  Assuredly 
those  which  are  best  fitted  to  live,  in  whatever  respect, 
or  respects,  their  superiority  of  fitness  may  consist. 
Hence  it  follows  that  Nature,  so  to  speak,  selects  the 
best  individuals  out  of  each  generation  to  1  i  ve.  And  not 
only  so ;  but  as  these  favoured  individuals  transmit 
their  favourable  qualities  to  their  offspring,  according  to 


260          Darwin,  and  after  Darwin. 

the  fixed  laws  of  heredity,  it  further  follows  that  the 
individuals  composing  each  successive  generation  have 
a  general  tendency  to  be  better  suited  to  their  sur- 
roundings than  were  their  forefathers.  And  this 
follows,  not  merely  because  in  every  generation  it  is 
only  the  "  flower  of  the  flock  "  that  is  allowed  to  breed, 
but  also  because,  if  in  any  generation  some  new  and 
beneficial  qualities  happen  to  arise  as  slight  variations 
from  the  ancestral  type  they  will  (other  things  per- 
mitting) be  seized  upon  by  natural  selection,  and,  being 
transmitted  by  heredity  to  subsequent  generations,  will 
be  added  to  the  previously  existing  type.  Thus  the 
best  idea  of  the  whole  process  will  be  gained  by  com- 
paring it  with  the  closely  analogous  process  whereby 
gardeners,  fanciers,  and  cattle-breeders  create  their 
wonderful  productions ;  for  just  as  these  men,  by 
always  "selecting"  their  best  individuals  to  breed 
from,  slowly  but  continuously  improve  their  stock,  so 
Nature,  by  a  similar  process  of  "selection"  slowly  but 
continuously  makes  the  various  species  of  plants  and 
animals  better  and  better  suited  to  the  conditions  of 
their  life. 

Now,  if  this  process  of  continuously  adapting  or- 
ganisms to  their  environment  takes  place  in  nature 
at  all,  there  is  no  reason  why  we  should  set  any  limits 
on  the  extent  to  which  it  is  able  to  go,  up  to  the 
point  at  which  a  complete  and  perfect  adaptation  is 
achieved.  Therefore  we  might  suppose  that  all  species 
would  eventually  reach  this  condition  of  perfect 
harmony  with  their  environment,  and  then  remain 
fixed.  And  so,  according  to  the  theory,  they  would, 
if  the  environment  were  itself  unchanging.  But  for- 
asmuch as  the  environment  (i.  e.  the  sum  total  of  the 


The  Theory  of  Natural  Selection.     261 

external  conditions  of  life)  of  almost  every  organic 
type  alters  more  or  less  from  century  to  century — 
whether  from  astronomical,  geological,  and  geographi- 
cal changes,  or  from  the  immigrations  and  emigrations 
of  other  species  living  on  contiguous  areas,  and  so 
bn — it  follows  that  the  process  of  natural  selection 
need  never  reach  a  terminal  phase.  And  forasmuch 
as  natural  selection  may  thus  continue,  ad  infinitum, 
slowly  to  alter  a  specific  type  in  adaptation  to  a 
gradually  changing  environment,  if  in  any  case  the 
alteration  thus  effected  is  sufficient  in  amount  to  lead 
naturalists  to  name  the  result  as  a  distinct  species, 
it  follows  that  natural  selection  has  transmuted  one 
specific  type  into  another.  Similarly,  by  a  continuation 
of  the  process,  specific  types  would  become  transmuted 
into  generic,  generic  into  family  types,  and  so  on.  Thus 
the  process  is  supposed  to  go  on  throughout  all  the 
countless  forms  of  life  continuously  and  simultaneously 
—the  world  of  organic  types  being  thus  regarded  as 
in  a  state  of  perpetual,  though  gradual,  flux. 

Now,  the  first  thing  we  have  to  notice  about  this 
theory  is,  that  in  all  its  main  elements  it  is  merely 
a  statement  of  observable  facts.  It  is  an  observable 
fact  that  in  all  species  of  plants  and  animals  a  very 
much  larger  number  of  individuals  are  born  than  can 
possibly  survive.  Thus,  for  example,  it  has  been 
calculated  that  if  the  progeny  of  a  single  pair  of 
elephants — which  are  the  slowest  breeding  of  animals 
— were  all  allowed  to  reach  maturity  and  propagate. 
in  750  years  there  would  be  living  19,000,000  de- 
scendants. Again,  in  the  case  of  vegetables,  if  a 
species  of  annual  plant  produces  only  two  seeds  a 


262  Darwin,  and  after  Darwin. 

year,  if  these  in  successive  years  were  all  allowed 
to  reproduce  their  kind,  in  twenty  years  there  would 
be  11,000,000  plants  from  a  single  ancestor.  Yet  we 
know  that  nearly  all  animals  and  plants  produce 
many  more  young  at  a  time  than  in  either  of  these 
two  supposed  cases.  Indeed,  as  individuals  of  many 
kinds  of  plants,  and  not  a  few  kinds  of  animals,  pro- 
duce every  year  several  thousand  young,  we  may  make 
a  rough  estimate  and  say,  that  over  organic  nature  as  a 
whole  probably  not  one  in  a  thousand  young  are  al- 
lowed to  survive  to  the  age  of  reproduction.  How 
tremendous,  therefore,  must  be  the  struggle  for  exis- 
tence !  It  is  thought  a  terrible  thing  in  battle  when 
one  half  the  whole  number  of  combatants  perish.  But 
what  are  we  to  think  of  a  battle  for  life  where  only 
one  in  a  thousand  survives  ? 

This,  then,  is  the  first  fact.  The  second  is  the  fact 
so  long  ago  recognised,  that  the  battle  is  to  the  strong, 
the  race  to  the  swift.  The  thousandth  individual 
which  does  survive  in  the  battle  for  existence — which 
does  win  the  race  for  life — is,  without  question,  one 
of  the  individuals  best  fitted  to  do  so ;  that  is  to  say, 
best  fitted  to  the  conditions  of  its  existence  considered 
as  a  whole.  Nature  is,  therefore,  always  picking  out, 
or  selecting,  such  individuals  to  live  and  to  breed. 

The  third  fact  is,  that  the  individuals  so  selected 
transmit  their  favourable  qualities  to  their  offspring 
by  heredity.  There  is  no  doubt  about  this  fact,  so 
far  as  we  are  concerned  with  it.  For  although,  as  I 
have  already  hinted,  considerable  doubt  has  of  late 
years  been  cast  upon  Lamarck's  doctrine  of  the 
hereditary  transmission  of  acquired  characters,  it 
remains  as  impossible  as  ever  it  was  to  question  the 


The   Theory  of  Natural  Selection.     263 

hereditary  transmission  of  what  are  called  congenital 
characters.  And  this  is  all  that  Darwin's  theory 
necessarily  requires. 

The  fourth  fact  is,  that  although  heredity  as  a  whole 
produces  a  wonderfully  exact  copy  of  the  parent  in 
the  child,  there  is  never  a  precise  reduplication.  Of 
all  the  millions  of  human  beings  upon  the  face  of  the 
earth,  no  one  is  so  like  another  that  we  cannot 
see  some  difference ;  the  resemblance  is  everywhere 
specific,  nowhere  individual.  Now  this  same  remark 
applies  to  all  specific  types.  The  only  reason  why 
we  notice  individual  differences  in  the  case  of  the 
human  type  more  than  we  do  in  the  case  of  any  other 
types,  is  because  our  attention  is  here  more  incessantly 
focussed  upon  these  differences.  We  are  compelled 
to  notice  them  in  the  case  of  our  own  species,  however 
small  they  may  appear  to  a  naturalist,  because,  unless 
we  do  so,  we  should  not  recognise  the  members  of  our 
own  family,  or  be  able  to  distinguish  between  a  man 
whom  we  know  is  ready  to  do  us  an  important  service, 
and  another  man  whom  we  know  is  ready  to  cut  our 
throats.  But  our  common  mother  Nature  is  able 
thus  to  distinguish  between  all  her  children.  Her 
eyes  are  much  more  ready  to  detect  small  individual 
peculiarities  than  are  the  eyes  of  any  naturalist.  No 
slight  variations  in  the  cast  of  feature  or  disposition 
of  parts,  no  minute  difference  in  the  arrangement  of 
microscopical  cells,  can  escape  her  ever  vigilant 
attention.  And,  consequently,  when  among  all  the 
innumerable  multitudes  of  individual  variations  any 
one  arises  which — no  matter  in  how  slight  a  degree — 
gives  to  that  individual  a  better  chance  of  success  in 
the  struggle  for  life,  Nature  chooses  that  individual 


264  Darwin,  and  after  Darwin. 

to  survive,  and  so  to  perpetuate  the  improvement  in 
his  or  her  progeny. 

Now  I  say  that  all  these  several  component  parts 
of  Darwinian  doctrine  are  not  matters  of  theory,  but 
matters  of  fact.  The  only  element  of  theory  in  his 
doctrine  of  evolution  by  natural  selection  has  reference 
to  the  degree  in  which  these  observable  facts,  when 
thus  brought  together,  are  adequate  to  account  for  the 
process  of  evolution. 

So  much,  then,  as  a  statement  of  the  theory  of 
natural  selection.  But  from  this  statement — i.  e.  from 
the  theory  of  natural  selection  itself — there  follow 
certain  matters  of  general  principle  which  it  is  im- 
portant to  bear  in  mind.  These,  therefore,  I  shall 
here  proceed  to  mention. 

First  of  all,  it  is  evident  that  the  theory  is  applicable 
as  an  explanation  of  organic  changes  in  specific  types 
only  in  so  far  as  these  changes  are  of  use,  or  so  far 
as  such  changes  endow  the  species  with  better  chances 
of  success  in  the  general  struggle  for  existence.  This 
is  the  only  sense  in  which  I  shall  always  employ  the 
terms  use,  utility,  service,  benefit  and  so  forth — that 
is  to  say,  in  the  sense  of  life-preserving. 

Next,  it  must  be  clearly  understood  that  the  life 
which  it  is  the  object,  so  to  speak,  of  natural  selection 
to  preserve,  is  primarily  the  life  of  the  species  ;  not 
that  of  the  individual.  Natural  selection  preserves 
the  life  of  the  individual  only  in  so  far  as  this  is 
conducive  to  that  of  the  species.  Wherever  the  life- 
interests  of  the  individual  clash  with  those  of  the 
species,  that  individual  is  sacrificed  in  favour  of  others 


The   Theory  of  Natural  Selection.     265 

who  happen  better  to  subserve  the  interests  of  the 
species.  For  example,  in  all  organisms  a  greater  or 
less  amount  of  vigour  is  wasted,  so  far  as  individual 
interests  are  concerned,  in  the  formation  and  the 
nourishment  of  progeny.  In  the  great  majority  of 
plants  and  animals  an  enormous  amount  of  physio- 
logical energy  is  thus  expended.  Look  at  the  roe  or 
the  milt  of  a  herring,  for  instance,  and  see  what  a 
huge  drain  has  been  made  upon  the  individual  for  the 
sake  of  its  species.  Again,  all  unselfish  instincts  have 
been  developed  for  the  sake  of  the  species,  and  usually 
against  the  interests  of  the  individual.  An  ant  which 
will  allow  her  head  to  be  slowly  drawn  from  her  body 
rather  than  relinquish  her  hold  upon  a  pupa,  is  clearly 
acting  in  response  to  an  instinct  which  has  been  de- 
veloped for  the  benefit  of  the  hive,  though  fatal  to  the 
individual.  And,  in  a  lesser  degree,  the  parental 
instincts,  wherever  they  occur,  are  more  or  less  de- 
trimental to  the  interests  of  the  individual,  though 
correspondingly  essential  to  those  of  the  race. 

These  illustrations  will  serve  to  show  that  natural 
selection  always  works  primarily  for  the  life-interests 
of  the  species — and,  indeed,  only  works  for  those  of 
the  individual  at  all  in  so  far  as  the  latter  happen  to 
coincide  with  the  former.  Or,  otherwise  stated,  the 
object  of  natural  selection  is  always  that  of  producing 
and  maintaining  specific  types  in  the  highest  degree 
of  efficiency,  no  matter  what  may  become  of  the  con- 
stituent individuals.  Which  is  a  striking  republication 
by  Science  of  a  general  truth  previously  stated  by 
Poetry : — 

So  careful  of  the  type  she  seems, 
So  careless  of  the  single  life. 


266          Darwin,  and  after  Darwin. 

Tennyson  thus  noted  the  fact,  and  a  few  years  later 
Darwin  supplied  the  explanation. 

But  of  course  in  many,  if  not  in  the  majority  of 
cases,  anything  that  adds  to  the  life-sustaining  power 
of  the  single  life  thereby  ministers  also  to  the  life- 
sustaining  power  of  the  type  ;  and  thus  we  can  under- 
stand why  all  mechanisms  and  instincts  which  minister 
to  the  single  life  have  been  developed— namely, 
because  the  life  of  the  species  is  made  up  of  the  lives 
of  all  its  constituent  individuals.  It  is  only  where 
the  interests  of  the  one  clash  with  those  of  the  other 
that  natural  selection  works  against  the  individual. 
So  long  as  the  interests  are  coincident,  it  works  in 
favour  of  both. 

Natural  selection,  then,  is  a  theory  which  seeks  to 
explain  by  natural  causes  the  occurrence  of  every  kind 
of  adaptation  which  is  to  be  met  with  in  organic 
nature,  on  the  assumption  that  adaptations  of  every 
kind  have  primary  reference  to  the  preservation  of 
species,  and  therefore  also,  as  a  general  rule,  to  the 
preservation  of  their  constituent  individuals.  And 
from  this  it  follows  that  where  it  is  for  the  benefit  of  a 
species  to  change  its  type,  natural  selection  will  effect 
that  change,  thus  leading  to  a  specific  transmutation, 
or  the  evolution  of  a  new  species.  In  such  cases 
the  old  species  may  or  may  not  become  extinct.  If 
the  transmutation  affects  the  species  as  a  whole,  or 
throughout  its  entire  range,  of  course  that  particular 
type  becomes  extinct,  although  it  does  so  by  becoming 
changed  into  a  still  more  suitable  type  in  the  -course 
of  successive  generations.  If,  on  the  other  hand, 
the  transmutation  affects  only  a  part  of  the  original 
species,  or  not  throughout  its  entire  range,  then  the 


The   Theory  of  Natural  Selection.     267 

other  parts  of  that  species  may  survive  for  any  number 
of  ages  as  they  originally  were.  In  the  one  case  there 
is  a  ladder-like  transmutation  of  species  in  time ;  in 
the  other  case  a  possibly  tree-like  multiplication  of 
species  in  space.  But  whether  the  evolution  of  spe- 
cies be  thus  serial  in  time  or  divergent  in  space,  the 
object  of  natural  selection,  so  to  speak,  is  in  either 
case  the  same — namely,  that  of  preserving  all  types 
which  prove  best  suited  to  the  conditions  of  their 
existence. 

Once  more,  the  term  "  struggle  for  existence  "  must 
be  understood  to  comprehend,  not  only  a  competition 
for  life  among  contemporary  individuals  of  the  same 
species,  but  likewise  a  struggle  by  all  such  individuals 
taken  collectively  for  the  continuance  of  their  own 
specific  type.  Thus,  on  the  one  hand,  while  there  is 
a  perpetual  civil  war  being  waged  between  members 
of  the  same  species,  on  the  other  hand  there  is  a 
foreign  war  being  waged  by  the  species  as  a  whole 
against  its  world  as  a  whole.  Hence  it  follows  that 
natural  selection  does  not  secure  survival  of  the  fittest 
as  regards  individuals  only,  but  also  survival  of  the 
fittest  as  regards  types.  This  is  a  most  important 
point  to  remember,  because,  as  a  general  rule,  these 
two  different  causes  produce  exactly  opposite  effects. 
Success  in  the  civil  war,  where  each  is  fighting  against 
all,  is  determined  by  individual  fitness  and  self-reliance. 
But  success  in  the  foreign  war  is  determined  by  what 
may  be  termed  tribal  fitness  and  mutual  dependence. 
For  example,  among  social  insects  the  struggle  for 
existence  is  quite  as  great  between  different  tribes  or 
communities,  as  it  is  between  different  individuals  of 


268          Darwin,  and  after  Darwin. 

the  same  community  ;  and  thus  we  can  understand 
the  extraordinary  degree  in  which  not  only  co- 
operative instincts,  but  also  largely  intelligent  social 
habits,  have  here  been  developed  \  Similarly,  in  the 
case  of  mankind,  we  can  understand  the  still  more  ex- 
traordinary development  of  these  things — culminating 
in  the  moral  sense.  I  have  heard  a  sermon,  preached 
at  one  of  the  meetings  of  the  British  Association, 
entirely  devoted  to  arguing  that  the  moral  sense  could 
not  have  been  evolved  by  natural  selection,  seeing 
that  the  altruism  which  this  sense  involves  is  the 
very  opposite  of  selfishness,  which  alone  ought  to  have 
been  the  product  of  survival  of  the  fittest  in  a  struggle 
for  life.  And,  of  course,  this  argument  would  have 
been  perfectly  sound  had  Darwin  limited  the  struggle 
for  existence  to  individuals,  without  extending  it  to 
communities.  But  if  the  preacher  had  ever  read 
Darwin's  works  he  would  have  found  that,  when  thus 
extended,  the  principle  of  natural  selection  is  bound 
to  work  in  favour  of  the  co-operative  instincts  in  the 
case  of  so  highly  social  an  animal  as  man  ;  and  that 
of  these  instincts  conscience  is  the  highest  imaginable 
exhibition. 

What  I  have  called  tribal  fitness — in  contra- 
distinction to  individual  fitness — begins  with  the 
family,  developes  in  the  community  (herd,  hive,  clan, 
&c.),  and  usually  ends  with  the  limits  of  the  species. 
On  the  one  hand,  however,  it  is  but  seldom  that  it 
extends  so  far  as  to  embrace  the  entire  species  ;  while, 
on  the  other  hand,  it  may  in  some  cases,  and  as  it  were 

1  For  cases,  see  Animal  Intelligence,  in  the  chapters  on  Ants  and 
Bees;  and,  for  discussion  of  principles,  Mental  Evolution  in  Animals. 
in  the  chapters  on  Instinct. 


The   Theory  of  Natural  Selection.     269 

sporadically,  extend  beyond  the  species.  In  these 
latter  cases  members  of  different  species  mutually 
assist  one  another,  whether  in  the  way  of  what  is 
called  symbiosis,  or  in  a  variety  of  other  ways  which 
I  need  not  wait  to  mention.  For  the  only  point 
which  I  now  desire  to  make  clear  is,  that  all  cases  of 
mutual  aid  or  co-operation,  whether  within  or  beyond 
the  limits  of  species,  are  cases  which  fall  under  the 
explanatory  sweep  of  the  Darwinian  theory1. 

Another  important  point  to  notice  is,  that  it  con- 
stitutes no  part,  of  the  theory  of  natural  selection  to 
suppose  that  survival  of  the  fittest  must  invariably 
lead  to  improvement  of  type,  in  the  sense  of  superior 
organization.  On  the  contrary,  if  from  change  of 
habits  or  conditions  of  life  an  organic  type  ceases  to 
have  any  use  for  previously  useful  organs,  natural 
selection  will  not  only  allow  these  organs  in  succes- 
sive generations  to  deteriorate — by  no  longer  placing 
any  selective  premium  upon  their  maintenance — but 
may  even  proceed  to  assist  the  agencies  engaged  in 
their  destruction.  For,  being  now  useless,  they  may 
become  even  deleterious,  by  absorbing  nutriment, 
causing  weight,  occupying  space,  &c.,  without  con- 
ferring any  compensating  benefit.  Thus  we  can  under- 
stand why  it  is  that  parasites,  for  example,  present  the 
phenomena  of  what  is  called  degeneration,  i.  e.  showing 
by  their  whole  structure  that  they  have  descended  from 
a  possibly  very  much  higher  type  of  organization  than 
that  which  they  now  exhibit.  Having  for  innumerable 

1  Prince  Kropotkin  in  the  Nineteenth  Century  (Feb.  1888,  Apr.  1891) 
has  adduced  a  large  and  interesting  body  of  facts,  showing  the  great 
prevalence  of  the  principle  of  co-operation  in  organic  nature. 


270          Darwin,  and  after  Darwin. 

generations  ceased  to  require  their  legs,  their  eyes, 
and  so  forth,  all  such  organs  of  high  elaboration  have 
either  disappeared  or  become  vestigial,  leaving  the 
parasite  as  a  more  or  less  effete  representative  of  its 
ancestry. 

These  facts  of  degeneration,  as  we  have  previously 
seen,  are  of  very  general  occurrence,  and  it  is  evident 
that  their  importance  in  the  field  of  organic  evolution 
as  a  whole  has  been  very  great.  Moreover,  it  ought  to 
be  particularly  observed  that,  as  just  indicated,  the  facts 
may  be  due  either  to  a  passive  cessation  of  selection,  or 
to  an  active  reversal  of  it.  Or,  more  correctly,  these 
facts  are  probably  always  due  to  the  cessation  of 
selection,  although  in  most  cases  where  species  in  a 
state  of  nature  are  concerned,  the  process  of  degener- 
ation has  been  both  hastened  and  intensified  by  the 
super-added  influence  of  the  reversal  of  selection.  In 
the  next  volume  I  shall  have  occasion  to  recur  to 
this  distinction,  when  it  will  be  seen  that  it  is  one  of 
no  small  importance  to  the  general  theory  of  descent. 

We  may  now  proceed  to  consider  certain  mis- 
conceptions of  the  Darwinian  theory  which  are  largely, 
not  to  say  generally,  prevalent  among  supporters  of 
the  theory.  These  misconceptions,  therefore,  differ 
from  those  which  fall  to  be  considered  in  the  next 
chapter,  i.  e.  misconceptions  which  constitute  grounds 
of  objection  to  the  theory. 

Of  all  the  errors  connected  with  the  theory  of 
natural  selection,  perhaps  the  one  most  frequently  met 
with — especially  among  supporters  of  the  theory — is 
that  of  employing  the  theory  to  explain  all  cases  of 


The   Theory  of  Natural  Selection.      2  7 1 

phyletic  modification  (or  inherited  change  of  type) 
indiscriminately,  without  waiting  to  consider  whether 
in  particular  cases  its  application  is  so  much  as 
logically  possible.  The  term  ';  natural  selection  "  thus 
becomes  a  magic  word,  or  Sesame,  at  the  utterance  of 
which  every  closed  door  is  supposed  to  be  immediately 
opened.  Be  it  observed,  I  am  not  here  alluding  to 
that  merely  blind  faith  in  natural  selection,  which  of 
late  years  has  begun  dogmatically  to  force  this 
principle  as  the  sole  cause  of  organic  evolution  in 
every  case  where  it  is  logically  possible  that  the  prin- 
ciple can  have  come  into  play.  Such  a  blind  faith, 
indeed,  I  hold  to  be  highly  inimical,  not  only  to  the 
progress  of  biological  science,  but  even  to  the  true 
interests  of  the  natural  selection  theory  itself.  As  to 
this  I  shall  have  a  good  deal  to  say  in  the  next 
volume.  Here,  however,  the  point  is,  that  the  theory 
in  question  is  often  invoked  in  cases  where  it  is  not 
even  logically  possible  that  it  can  apply,  and  therefore 
in  cases  where  its  application  betokens,  not  merely  an 
error  of  judgment  or  extravagance  of  dogmatism,  but  a 
fallacy  of  reasoning  in  the  nature  of  a  logical  contra- 
diction. Almost  any  number  of  examples  might  be 
given ;  but  one  will  suffice  to  illustrate  what  is  meant. 
And  I  choose  it  from  the  writings  of  one  of  the 
authors  of  the  selection  theory  itself,  in  order  to  show 
how  easy  it  is  to  be  cheated  by  this  mere  juggling 
with  a  phrase — for  of  course  I  do  not  doubt  that  a 
moment's  thought  would  have  shown  the  writer  the 
untenability  of  his  statement. 

In  his  most  recent  work  Mr.  Wallace  advances  an 
interesting  hypothesis  to  the  effect  that  differences  of 
colour  between  allied  species,  which  are  apparently 


272          Darwin,  and  after  Darwin. 

too  slight  to  serve  any  other  purpose,  may  act  as 
"  recognition  marks,"  whereby  the  opposite  sexes  are 
enabled  at  once  to  distinguish  between  members  of 
their  own  and  of  closely  resembling  species.  Of 
course  this  hypothesis  can  only  apply  to  the  higher 
animals ;  but  the  point  here  is  that,  supposing  it  to 
hold  for  them.  Mr.  Wallace  proceeds  to  argue  thus  : — 
Recognition  marks  "have  in  all  probability  been 
acquired  in  the  process  of  differentiation  for  the 
purpose  of  checking  the  intercrossing  of  allied  forms," 
because c;  one  of  the  first  needs  of  a  new  species  would 
be  to  keep  separate  from  its  nearest  allies,  and  this 
could  be  more  readily  done  by  some  easily  seen 
external  mark 1."  Now,  it  is  clearly  not  so  much 
as  logically  possible  that  these  recognition-marks 
(supposing  them  to  be  such)  can  have  been  acquired 
by  natural  selection,  "  for  the  purpose  of  checking 
intercrossing  of  allied  forms."  For  the  theory  of 
natural  selection,  from  its  own  essential  nature  as  a 
theory,  is  logically  exclusive  of  the  supposition  that 
survival  of  the  fittest  ever  provides  changes  in  antici- 
pation of  future  uses.  Or,  otherwise  stated,  it  involves 
a  contradiction  of  the  theory  itself  to  say  that  the 
colour-changes  in  question  were  originated  by  natural 
selection,  in  order  to  meet  "  one  of  \hefirst  needs  of  a 
new  species,"  or  for  the  purpose  of.  subsequently 
preventing  intercrossing  with  allied  forms.  If  it  had 
been  said  that  these  colour-differentiations  were 
originated  by  some  cause  other  than  natural  selection 
(or,  if  by  natural  selection,  still  with  regard  to  some 
previous,  instead  of  prophetic, "  purpose  "),  and,  when  so 
"  acquired,"  then  began  to  serve  the  "  purpose"  assigned, 

1  Darwinism,  pp.  218  and  227. 


The  Theory  of  Natural  Selection.     273 

the  argument  would  not  have  involved  the  fallacy 
which  we  are  now  considering.  But,  as  it  stands,  the 
argument  reverts  to  the  teleology  of  pre-Darwinian 
days — or  the  hypothesis  of  a  "  purpose  "  in  the  literal 
sense  which  sees  the  end  from  the  beginning,  instead 
of  a  "  purpose  "  in  the  metaphorical  sense  of  an  adap- 
tation that  is  evolved  by  the  very  modifications  which 
subserve  it  \ 

Another  very  prevalent,  and  more  deliberate,  fallacy 
connected  with  the  theory  of  natural  selection  is,  that 
it  follows  deductively  from  the  theory  itself  that  the 
principle  of  natural  selection  must  be  the  sole  means 
of  modification  in  all  cases  where  modification  is  of 
an  adaptive  kind, — with  the  consequence  that  no 
other  principle  can  ever  have  been  concerned  in  the 
production  of  structures  or  instincts  which  are  of  any 
use  to  their  possessors.  Whether  or  not  natural 
selection  actually  has  been  the  sole  means  of  adaptive 
modification  in  the  race,  as  distinguished  from  the 
individual,  is  a  question  of  biological  fact2;  but  it 


1  Since  the  above  was  written  Prof.  Lloyd  Morgan  has  published  a 
closely  similar  notice  of  the  passage  in  question.     "  This  language,"  he 
says,  "seems  to  savour  of  teleology  (that  pitfall  of  the  evolutionist). 
The  cart  is  put   before  the  horse.  ^    The   recognition-marks  were,    I 
believe,  not  produced   to   prevent  intercrossing,  but  intercrossing  has 
been   prevented   because   of   preferential   mating    between   individuals 
possessing  special  recognition-marks.     To  miss  this  point  is  to  miss 
an  important  segregation-factor."— (Animal  Life  and  Intelligence,  p. 
103.)     Again,  on  pp.  184-9,  ^e  furnishes  an  excellent  discussion  on  the 
whole  subject  of  the  fallacy  alluded  to  in  the  text,  and  gives  illustrative 
quotations  from  other  prominent  Darwinians.     I  should  like   to  add 
that  Darwin  himself  has  nowhere  fallen  into  this,  or  any  of  the  other 
fallacies,  which  are  mentioned  in  the  text. 

2  Of  course  adaptive  modifications  produced  in  the  individual  life- 
time, and  not  inherited,  do  not  concern  the  question  at  all.     In  this  and 


274          Darwin,  and  ajter  Darwin. 

involves  a  grave  error  of  reasoning  to  suppose  that 
this  question  can  be  answered  deductively  from  the 
theory  of  natural  selection  itself,  as  I  shall  show  at 
some  length  in  the  next  volume. 

A  still  more  extravagant,  and  a  still  more  un- 
accountable fallacy  is  the  one  which  represents  it  as 
following  deductively  from  the  theory  of  natural 
selection  itself,  that  all  hereditary  characters  are 
"  necessarily "  due  to  natural  selection.  In  other 
words,  not  only  all  adaptive,  but  likewise  all  non- 
adaptive  hereditary  characters,  it  is  said,  must  be  due 
to  natural  selection.  For  non-adaptive  characters  are 
taken  to  be  due  to  "correlation  of  growth,"  in  con- 
nexion with  some  of  the  adaptive  ones — natural 
selection  being  thus  the  indirect  means  of  producing 
the  former  wherever  they  may  occur,  on  account  of  its 
being  the  direct  and  the  only  means  of  producing  the 
latter.  Thus  it  is  deduced  from  the  theory  of  natural 
selection  itself, — ist.  that  the  principle  of  natural 
selection  is  the  only  possible  cause  of  adaptive  modifi- 
cation :  and,  that  non-adaptive  modifications  can  only 
occur  in  the  race  as  correlated  appendages  to  the 
adaptive :  3rd,  that,  consequently,  natural  selection  is 
the  only  possible  cause  of  modification,  whether 
adaptive  or  non-adaptive.  Here  again,  therefore,  we 
must  observe  that  none  of  these  sweeping  general- 
izations can  possibly  be  justified  by  deductive  reasoning 
from  the  theory  of  natural  selection  itself.  Any  attempt 
at  such  deductive  reasoning  must  necessarily  end  in 
circular  reasoning,  as  I  shall  likewise  show  in  the 

the  following  paragraphs,  therefore,  "  adaptations,"  "  adaptive  modifica- 
tions," &c.,  refer  exclusively  to  such  as  are  hereditary,  i.  e.  phyletic. 


The   T/ieory  of  Natural  Selection.     275 

second  volume,  where  this  whole  "question  of  utility" 
will  be  thoroughly  dealt  with. 

Once  more,  there  is  an  important  oversight  very 
generally  committed  by  the  followers  of  Darwin.  For 
even  those  who  avoid  the  fallacies  above  mentioned 
often  fail  to  perceive,  that  natural  selection  can  only 
begin  to  operate  if  the  degree  of  adaptation  is  already 
given  as  sufficiently  high  to  count  for  something  in  the 
struggle  for  existence.  Any  adaptations  which  fall 
below  this  level  of  importance  cannot  possibly  have 
been  produced  by  survival  of  the  fittest.  Yet  the 
followers  of  Darwin  habitually  speak  of  adaptative 
characters,  which  in  their  oivn  opinion  are  subservient 
merely  to  comfort  or  convenience,  as  having  been 
produced  by  such  means.  Clearly  this  is  illogical ; 
for  it  belongs  to  the  essence  of  Darwin's  theory  to 
suppose,  that  natural  selection  can  have  no  jurisdiction 
beyond  the  line  where  structures  or  instincts  already 
present  a  sufficient  degree  of  adaptational  value  to 
increase,  in  some  measure,  the  expectation  of  life  on 
the  part  of  their  possessors.  We  cannot  speak  of 
adaptations  as  due  to  natural  selection,  without 
thereby  affirming  that  they  present  what  I  have  else- 
where termed  a  "  selection  value." 

Lastly,  as  a  mere  matter  of  logical  definition,  it  is 
well-nigh  self-evident  that  the  theory  of  natural 
selection  is  a  theory  of  the  origin,  and  cumulative 
development,  of  adaptations,  whether  these  be  distinc- 
tive of  species,  or  of  genera,  orders,  families,  classes, 
and  sub-kingdoms.  It  is  only  when  the  adaptations 
happen  to  be  distinctive  of  the  first  (or  lowest)  of  these 
T  - 


276          Darwin,  and  after  Darwin. 

taxonomic  divisions,  that  the  theory  which  accounts 
for  these  adaptations  accounts  also  for  the  forms  which 
present  them,— i.  e.  becomes  also  a  theory  of  the  origin 
of  species.  This,  however,  is  clearly  but  an  accident  of 
particular  cases ;  and,  therefore,  even  in  them  the 
theory  is  primarily  a  theory  of  adaptations,  while  it  is 
but  secondarily  a  theory  of  the  species  which  present 
them.  Or,  otherwise  stated,  the  theory  is  no  more  a 
theory  of  the  origin  of  species  than  it  is  of  the  origin 
of  genera,  families,  and  the  rest ;  while,  on  the  other 
hand,  it  is  everywhere  a  theory  of  the  adaptive  modifi- 
cations whereby  each  of  these  taxonomic  divisions  has 
been  differentiated  as  such.  Yet,  sufficiently  obvious 
as  the  accuracy  of  this  definition  must  appear  to  any 
one  who  dispassionately  considers  it, several  naturalists 
of  high  standing  have  denounced  it  in  violent  terms. 
I  shall  therefore  have  to  recur  to  the  subject  at  some- 
what greater  length  hereafter.  At  present  it  is  enough 
merely  to  mention  the  matter,  as  furnishing  another 
and  a  curious  illustration  of  the  not  infrequent 
weakness  of  logical  perception  on  the  part  of  minds 
well  gifted  with  the  faculty  of  observation.  It  may  be 
added,  however,  that  the  definition  in  question  is  in 
no  way  hostile  to  the  one  which  is  virtually  given  by 
Darwin  in  the  title  of  his  great  work.  The  Origin  of 
Species  by  means  of  Natural  Selection  is  beyond 
doubt  the  best  title  that  could  have  been  given, 
because  at  the  time  when  the  work  was  published  the 
fact,  no  less  than  the  method,  of  organic  evolution  had 
to  be  established ;  and  hence  the  most  important 
thing  to  be  done  at  that  time  was  to  prove  the 
transmutation  of  species.  But  now  that  this  has  been 
done  to  the  satisfaction  of  naturalists  in  general,  it  is; 


The   Theory  of  Natural  Selection.     277 

as  I  have  said,  curious  to  find  some  of  them  denouncing 
a  wider  definition  of  the  principle  of  natural  selection, 
merely  because  the  narrower  (or  included)  definition  is 
invested  with  the  charm  of  verbal  associations a. 

So  much  for  fallacies  and  misconceptions  touch- 
ing Darwin's  theory,  which  are  but  too  frequently 
met  with  in  the  writings  of  its  supporters.  We  must 
now  pass  on  to  mention  some  of  the  still  greater 
fallacies  and  misconceptions  which  are  prevalent  in 
the  writings  of  its  opponents.  And,  in  order  to  do 
this  thoroughly,  I  shall  begin  by  devoting  the  re- 
mainder of  the  present  chapter  to  a  consideration  of 
the  antecedent  standing  of  the  two  theories  of  natural 
selection  and  supernatural  design.  This  having  been 
done,  in  the  succeeding  chapters  I  shall  deal  with  the 
evidences  for,  and  the  objections  against,  the  former 
theory. 

Beginning,  then,  with  the  antecedent  standing  oi 
these  alternative  theories,  the  first  thing  to  be  noticed 
is,  that  they  are  both  concerned  with  the  same  subject- 
matter,  which  it  is  their  common  object  to  explain. 
Moreover,  this  subject-matter  is  clearly  and  sharply 
divisible  into  two  great  classes  of  facts  in  organic 
nature — namely,  those  of  Adaptation  and  those  of 
Beauty.  Darwin's  theory  of  descent  explains  the  for- 
mer by  his  doctrine  01  natural  selection,  and  the  latter 
by  his  doctrine  of  sexual  selection.  In  the  first  instance, 
therefore,  I  shall  have  to  deal  only  with  the  facts  of 

1  The  question  as  to  whether  natural  selection  has  been  the  only  prin 
ciple  concerned  in  the  origination  oi  species,  is  quite  distinct  from  that 
as  to  the  accuracy  of  the  above  definition. 


278          Darwin,  and  after  Darwin. 

adaptation,  leaving  for  subsequent  consideration  the 
facts  of  beauty. 

Innumerable  cases  of  the  adaptation  of  organisms 
to  their  surroundings  being  the  facts  which  now  stand 
before  us  to  be  explained  either  by  natural  selection 
or  by  supernatural  intention,  we  may  first  consider  a 
statement  which  is  frequently  met  with — namely,  that 
even  if  all  such  cases  of  adaptation  were  proved  to 
be  fully  explicable  by  the  theory  of  descent,  this 
would  constitute  no  disproof  of  the  theory  of  design : 
all  the  cases  of  adaptation,  it  is  argued,  might  still 
be  due  to  design,  even  though  they  admit  of  being 
hypothetically  accounted  for  by  the  theory  of  descent 
I  have  heard  an  eminent  Professor  tell  his  class  that 
the  many  instances  of  mechanical  adaptation  discovered 
and  described  by  Darwin  as  occurring  in  onehids, 
seemed  to  him  to  furnish  better  proof  of  supernatural 
contrivance  than  of  natural  causes  ;  and  another  emi- 
nent Professor  has  informed  me  that,  although  he  had 
read  the  Origin  of  Species  with  care,  he  could  see  in 
it  no  evidence  of  natural  selection  which  might  not 
equally  well  have  been  adduced  in  favour  of  intelligent 
design.  But  here  we  meet  with  a  radical  misconception 
of  the  whole  logical  attitude  of  science.  For,  be  it 
observed,  this  exception  in  limine  to  the  evidence 
which  we  are  about  to  consider  does  not  question  that 
natural  selection  may  be  able  to  do  all  that  Darwin 
ascribes  to  it  The  objection  is  urged  against  his 
interpretation  of  the  facts  merely  on  the  ground  that 
these  facts  might  equally  well  be  ascribed  to  intelligent 
design.  And  so  undoubtedly  they  might,  if  we  were 
all  simple  enough  to  adopt  a  supernatural  explana- 
tion whenever  a  natural  one  is  found  sufficient  to 


The   Theory  of  Natural  Selection.      279 

account  for  the  facts.  Once  admit  the  irrational 
principle  that  we  may  assume  the  operation  of  higher 
causes  where  the  operation  of  lower  ones  is  sufficient 
to  explain  the  observed  phenomena,  and  all  our  science 
and  all  our  philosophy  are  scattered  to  the  winds. 
For  the  law  of  logic  which  Sir  William  Hamilton 
called  the  law  of  parsimony — or  the  law  which  forbids 
us  to  assume  the  operation  of  higher  causes  when  lower 
ones  are  found  sufficient  to  explain  the  observed 
effects — this  law  constitutes  the  only  barrier  between 
science  and  superstition.  It  is  always  possible  to  give 
a  hypothetical  explanation  of  any  phenomenon  what- 
soever, by  referring  it  immediately  to  the  intelligence 
of  some  supernatural  agent ;  so  that  the  only  difference 
between  the  logic  of  science  and  the  logic  of  superstition 
consists  in  science  recognising  a  validity  in  the  law  of 
parsimony  which  superstition  disregards.  Therefore 
one  can  have  no  hesitation  in  saying  that  this  way 
of  looking  at  the  evidence  in  favour  of  natural  selection 
is  not  a  scientific  or  a  reasonable  way  of  looking  at  it, 
but  a  purely  superstitious  way.  Let  us  take,  as  an 
illustration,  a  perfectly  parallel  case.  When  Kepler 
was  unable  to  explain  by  any  known  causes  the  paths 
described  by  the  planets,  he  resorted  to  a  supernatural 
explanation,  and  supposed  that  every  planet  was  guided 
in  its  movements  by  some  presiding  angel.  But  when 
Newton  supplied  a  beautifully  simple  physical  ex- 
planation, all  persons  with  a  scientific  habit  of  mind 
at  once  abandoned  the  metaphysical  one.  Now,  to 
be  consistent,  the  above-mentioned  Professors,  and  all 
who  think  with  them,  ought  still  to  adhere  to  Kepler's 
hypothesis  in  preference  to  Newton's  explanation; 
for,  excepting  the  law  of  parsimony,  there  is  certainly 


280          Darwin,  and  after  Darwin. 

no  other  logical  objection  to  the  statement,  that  the 
movements  of  the  planets  afford  as  good  evidence  of 
the  influence  of  guiding  angels  as  they  do  of  the  in- 
fluence of  gravitation. 

So  much,  then,  for  the  illogical  position  that,  granting 
the  evidence  in  favour  of  natural  descent  and  super- 
natural design  to  be  equal  and  parallel,  we  should 
hesitate  in  our  choice  between  the  two  theories.  But, 
of  course,  if  the  evidence  is  supposed  not  to  be  equal 
and  parallel — i.  e.  if  it  is  supposed  that  the  theory  of 
natural  selection  is  not  so  good  a  theory  whereby  to 
explain  the  facts  of  adaptation  as  is  that  of  super- 
natural design, — then  the  objection  is  no  longer  the  one 
which  we  are  considering.  It  is  quite  another  objection, 
and  one  which  is  not  prima  facie  absurd.  Therefore 
let  us  state  clearly  the  distinct  question  which  thus 
arises. 

Innumerable  cases  of  adaptation  of  organisms  to 
their  environments  are  the  observed  facts  for  which  an 
explanation  is  required.  To  supply  this  explanation, 
two,  and  only  two,  hypotheses  are  in  the  field.  Of 
these  two  hypotheses  one  is  intelligent  design  mani- 
fested directly  in  special  creation  ;  the  other  is  natural 
causation  operating  through  countless  ages  of  the  past. 
Now,  the  adaptations  in  question  involve  an  innumer- 
able multitude  of  special  mechanisms,  in  most  cases 
even  within  the  limits  of  any  one  given  species  ;  but 
when  we  consider  the  sum  of  all  these  mechanisms 
presented  by  organic  nature  as  a  whole,  the  mind 
must  indeed  be  dull  which  does  not  feel  astounded. 
For,  be  it  further  observed,  these  mechanical  con- 
trivances1 are,  for  the  most  part,  no  merely  simple 

1  It  is  often  objected  to  Darwin's  terminology,  that  it  embraces  such 


The  Theory  of  Natural  Selection.     28 1 

arrangements,  which  might  reasonably  be  supposed 
due,  like  the  phenomena  of  crystallization,  to  com- 
paratively simple  physical  causes.  On  the  contrary, 
they  everywhere  and  habitually  exhibit  so  deep-laid, 
so  intricate,  and  often  so  remote  an  adaptation  of 
means  to  ends,  that  no  machinery  of  human  contrivance 
can  properly  be  said  to  equal  their  perfection  from  a 
mechanical  point  of  view.  Therefore,  without  question, 
the  hypothesis  which  first  of  all  they  suggest— or 
suggest  most  readily — is  the  hypothesis  of  design. 
And  this  hypothesis  becomes  virtually  the  only  hypo- 
thesis possible,  if  it  be  assumed — as  it  generally  was 
assumed  by  natural  theologians  of  the  past, — that  all 
species  of  plants  and  animals  were  introduced  into 
the  world  suddenly.  For  it  is  quite  inconceivable  that 
any  known  cause,  other  than  intelligent  design,  could 
be  competent  to  turn  out  instantaneously  any  one  of 
these  intricate  pieces  of  machinery,  already  adapted 
to  the  performance  of  its  special  function.  But,  on  the 
other  hand,  if  there  is  any  evidence  to  show  that  one 
species  becomes  slowly  transformed  into  another — 
or  that  one  set  of  adaptations  becomes  slowly  changed 
into  another  set  as  changing  circumstances  require, — 
then  it  becomes  quite  possible  to  imagine  that  a 
strictly  natural  causation  may  have  had  something 
to  do  with  the  matter.  And  this  suggestion  becomes 
greatly  more  probable  when  we  discover,  from  geo- 
logical evidence  and  embryological  research,  that  in 
the  history  both  of  races  and  of  individuals  the 

words  as  "contrivance,"  "purpose,"  &c.,  which  are  strictly  applicable 
only  to  the  processes  or  the  products  of  thought.  But  when  it  is  under- 
stood that  they  are  used  in  a  neutral  or  metaphorical  sense,  I  cannot  see 
that  any  harm  arises  from  their  use. 


282          Darwin,  and  after  Darwin. 

various  mechanisms  in  question  have  themselves  had 
a  history — beginning  in  the  forms  of  most  uniformity 
and  simplicity,  gradually  advancing  to  forms  more 
varied  and  complex,  nowhere  exhibiting  any  inter- 
ruptions in  their  upward  progress,  until  the  world  of 
organic  machinery  as  we  now  have  it  is  seen  to  have 
been  but  the  last  phase  of  a  long  and  gradual  growth, 
the  ultimate  roots  of  which  are  to  be  found  in  the  soil 
of  undifferentiated  protoplasm. 

Lastly,  when  there  is  supplied  to  us  the  suggestion 
of  natural  selection  as  a  cause  presumably  adequate  to 
account  for  this  continuous  growth  in  the  number,  the 
intricacy,  and  the  perfection  of  such  mechanisms,  it  is 
only  the  most  unphilosophical  mind  that  can  refuse  to 
pause  as  between  the  older  hypothesis  of  design  and 
the  newer  hypothesis  of  descent. 

Thus  it  is  clear  that  the  a  priori  standing  of  the 
rival  hypotheses  of  naturalism  and  supernaturalism  in 
the  case  of  all  these  pieces  of  organic  machinery,  is 
profoundly  affected  by  the  question  whether  they  came 
into  existence  suddenly,  or  whether  they  did  so  grad- 
ually. For,  if  they  all  came  into  existence  suddenly, 
the  fact  would  constitute  well-nigh  positive  proof 
in  favour  of  supernaturalism,  or  creation  by  design  ; 
whereas,  if  they  all  came  into  existence  gradually,  this 
fact  would  in  itself  constitute  presumptive  evidence  in 
favour  of  naturalism,  or  of  development  by  natural 
causes.  And,  as  shown  in  the  previous  chapters, 
the  proof  that  all  species  of  plants  and  animals  came 
into  existence  gradually — or  the  proof  of  evolution  as 
a  fact — is  simply  overwhelming. 

From  a  still  more  general  point  of  view  I  may  state 
the  case  in  another  way,  by  borrowing  and  somewhat 


The  Theory  of  Natural  Selection.      283 

expanding  an  illustration  which,  I  believe,  was  first 
used  by  Professor  Huxley.  If,  when  the  tide  is  out,  we 
see  lying  upon  the  shore  a  long  line  of  detached  sea- 
weed, marking  the  level  which  is  reached  by  full  tide, 
we  should  be  free  to  conclude  that  the  separation  of 
the  sea-weed  from  the  sand  and  the  stones  was  due 
to  the  intelligent  work  of  some  one  who  intended  to 
collect  the  sea-weed  for  manure,  or  for  any  other  pur- 
pose. But,  on  the  other  hand,  we  might  explain  the 
fact  by  a  purely  physical  cause — namely,  the  separa- 
tion by  the  sea-waves  of  the  sea-weed  from  the  sand 
and  stones,  in  virtue  of  its  lower  specific  gravity.  Now, 
thus  far  the  fact  would  be  explained  equally  well  by 
either  hypothesis ;  and  this  fact  would  be  the  fact  of 
selection.  But  whether  we  yielded  our  assent  to  the 
one  explanation  or  to  the  other  would  depend  upon  a 
due  consideration  of  all  collateral  circumstances.  The 
sea-weed  might  not  be  of  a  kind  that  is  of  any  use  to 
man ;  there  might  be  too  great  a  quantity  of  it  to 
admit  of  our  supposing  that  it  had  been  collected  by 
man ;  the  fact  that  it  was  all  deposited  on  the  high- 
water-mark  would  in  itself  be  highly  suggestive  of  the 
agency  of  the  sea  ;  and  so  forth.  Thus,  in  such  a  case 
any  reasonable  observer  would  decide  in  favour  of  the 
physical  explanation,  or  against  the  teleological  one. 

Now  the  question  whether  organic  evolution  has 
been  caused  by  physical  agencies  or  by  intelligent 
design  is  in  precisely  the  same  predicament.  There 
can  be  no  logical  doubt  that,  theoretically  at  all  events, 
the  physical  agencies  which  the  present  chapter  is  con- 
cerned with,  and  which  are  conveniently  summed  up  in 
the  term  natural  selection,  are  as  competent  to  produce 
these  so-called  mechanical  contrivances,  and  the  other 


284          Darwin,  and  after  Darwin. 

cases  of  adaptation  which  are  to  be  met  with  in  organic 
nature,  as  intelligent  design  could  be.  Hence,  our 
choice  as  between  these  two  hypotheses  must  be  go- 
verned by  a  study  of  all  collateral  circumstances  ;  that 
is  to  say,  by  a  study  of  the  evidences  in  favour  of  the 
physical  explanation.  To  this  study,  therefore,  we 
shall  now  address  ourselves,  in  the  course  of  the  follow- 
ing chapters. 


CHAPTER   VIII. 

EVIDENCES  OF  THE  THEORY  OF  NATURAL 
SELECTION. 

I  WILL  now  proceed  to  state  the  main  arguments  in 
favour  of  the  theory  of  natural  selection,  and  then,  in 
the  following  chapter,  the  main  objections  which  have 
been  urged  against  it. 

In  my  opinion,  the  main  arguments  in  favour  of  the 
theory  are  three  in  number. 

First,  it  is  a  matter  of  observation  that  the  struggle 
for  existence  in  nature  does  lead  to  the  extermination 
of  forms  less  fitted  for  the  struggle,  and  thus  makes 
room  for  forms  more  fitted.  This  general  fact  may  be 
best  observed  in  cases  where  an  exotic  species  proves 
itself  better  fitted  to  inhabit  a  new  country  than  is  some 
endemic  species  which  it  exterminates.  In  Great 
Britain,  for  example,  the  so-called  common  rat  is  a 
comparatively  recent  importation  from  Norway,  and 
it  has  so  completely  supplanted  the  original  British  rat, 
that  it  is  now  extremely  difficult  to  procure  a  single 
specimen  of  the  latter  :  the  native  black  rat  has  been 
all  but  exterminated  by  the  foreign  brown  rat.  The 
same  thing  is  constantly  found  in  the  case  of  imported 
species  of  plants.  I  have  seen  the  river  at  Cambridge 
so  choked  with  the  inordinate  propagation  of  a  species 


286          Darwin,  and  after  Darwin. 

of  water-weed  which  had  been  introduced  from 
America,  that  considerable  expense  had  to  be  incurred 
in  order  to  clear  the  river  for  traffic.  In  New  Zealand 
the  same  thing  has  happened  with  the  European 
water-cress,  and  in  Australia  with  the  common  rabbit. 
So  it  is  doubtless  true,  as  one  of  the  natives  is  said  to 
have  philosophically  remarked,  "  the  white  man's  rat 
has  driven  away  our  rat,  the  European  fly  drives  away 
our  fly,  his  clover  kills  our  grass,  and  so  will  the  Maoris 
disappear  before  the  white  man  himself."  Innumer- 
able other  cases  to  the  same  effect  might  be  quoted  ; 
and  they  all  go  to  establish  the  fact  that  forms  less 
fitted  to  survive  succumb  in  their  competition  with 
forms  better  fitted. 

Secondly,  there  is  a  general  consideration  of  the 
largest  possible  significance  in  the  present  connexion — 
namely,  that  among  all  the  millions  of  structures  and 
instincts  wh:ch  are  so  invariably,  and  for  the  most  part 
so  wonderfully,  adapted  to  the  needs  of  the  species 
presenting  them,  we  cannot  find  a  single  instance, 
either  in  the  vegetable  or  animal  kingdom,  of  a 
structure  or  an  instinct  which  is  developed  for  the 
exclusive  benefit  of  another  species.  Now  this  great 
and  general  fact  is  to  my  mind  a  fact  of  the  most 
enormous,  not  to  say  overwhelming,  significance.  The 
theory  of  natural  selection  has  now  been  before  the 
world  for  more  than  thirty  years,  and  during  that  time 
it  had  stood  a  fire  of  criticism  such  as  was  never  en- 
countered by  any  scientific  theory  before.  From  the 
first  Darwin  invited  this  criticism  to  adduce  any  single 
instance,  either  in  the  vegetable  or  animal  kingdom,  of 
a  structure  or  an  instinct  which  should  unquestionably 


Evidences  of  Theory  of  Natural  Selection.   287 

be  proved  to  be  of  exclusive  use  to  any  species  other 
than  the  one  presenting  it.  He  even  went  so  far  as  to 
say  that  if  any  one  such  instance  could  be  shown  he 
would  surrender  his  whole  theory  on  the  strength  of 
it — so  assured  had  he  become,  by  his  own  prolonged 
researches,  that  natural  selection  was  the  true  agent 
in  the  production  of  adaptive  structures,  and,  as  such, 
could  never  have  permitted  such  a  structure  to  occur 
in  one  species  for  the  benefit  of  another.  Now,  as  this 
invitation  has  been  before  the  world  for  so  many  years, 
and  has  not  yet  been  answered  by  any  naturalist,  we 
may  by  this  time  be  pretty  confident  that  it  never  will 
be  answered.  How  tremendous,  then,  is  the  significance 
of  this  fact  in  its  testimony  to  Darwin's  theory !  The 
number  of  animal  and  vegetable  species,  both  living 
and  extinct,  is  to  be  reckoned  by  millions,  and  every 
one  of  these  species  presents  on  an  average  hundreds  of 
adaptive  structures, — at  least  one  of  which  in  many, 
possibly  in  most,  if  not  actually  in  all  cases,,  is  peculiar 
to  the  species  that  presents  it.  In  other  words,  there 
are  millions  of  adaptive  structures  (not  to  speak  of  in- 
stincts) which  are  peculiar  to  the  species  presenting 
them,  and  also  many  more  which  are  the  common 
property  of  allied  species :  yet,  notwithstanding  this 
inconceivable  profusion  of  adaptive  structures  in 
organic  nature,  there  is  no  single  instance  that  has 
been  pointed  out  of  the  occurrence  of  such  a  structure 
save  for  the  benefit  of  the  species  that  presents  it. 
Therefore,  I  say  that  this  immensely  large  and  general 
fact  speaks  with  literally  immeasurable  force  in  favour 
of  natural  selection,  as  at  all  events  one  of  the  main 
causes  of  organic  evolution.  For  the  fact  is  precisely 
what  we  should  expect  if  this  theory  is  true,  while 


288          Darwin,  and  after  Darwin. 

upon  no  other  theory  can  its  universality  and  invari- 
ability be  rendered  intelligible.  On  the  beneficent 
design  theory,  for  instance,  it  is  inexplicable  that  no 
species  should  ever  be  found  to  present  a  structure  or 
an  instinct  having  primary  reference  to  the  welfare  of 
another  species,  when,  ex  hypothesi,  such  an  endless 
amount  of  thought  has  been  displayed  in  the  creation 
of  structures  and  instincts  having  primary  reference  to 
the  species  which  present  them.  For  how  magnificent 
a  display  of  divine  beneficence  would  organic  nature 
have  afforded,  if  all — or  even  some — species  had  been 
so  inter-related  as  to  have  ministered  to  each  others 
wants.  Organic  species  might  then  have  been  likened 
to  a  countless  multitude  of  voices,  all  singing  in  one 
great  harmonious  psalm.  But,  as  it  is,  we  see  abso- 
lutely no  vestige  of  such  co-ordination  :  every  species 
is  for  itself,  and  for  itself  alone — an  outcome  of  the 
always  and  everywhere  fiercely  raging  struggle  for 
life. 

In  order  that  the  force  of  this  argument  may  not  be 
misapprehended,  it  is  necessary  to  bear  in  mind  that 
it  is  in  no  way  affected  by  cases  where  a  structure  or 
an  instinct  is  of  primary  benefit  to  its  possessor,  and 
then  becomes  of  secondary  benefit  to  some  other  species 
on  account  of  the  latter  being  able  in  some  way  or 
another  to  utilise  its  action.  Of  course  organic  nature 
is  full  of  cases  of  this  kind  ;  but  they  only  go  to  show 
the  readiness  which  all  species  display  to  utilise  for 
themselves  everything  that  can  be  turned  to  good  ac- 
count in  their  own  environments,  and  so,  among  other 
things,  the  structures  and  instincts  of  other  animals.  For 
instance,  it  would  be  no  answer  to  Darwin's  challenge  if 
any  one  were  to  point  to  a  hermit-crab  inhabiting  the 


Evidences  of  Theory  of  Natural  Selection.  289 

cast-off  shell  of  a  mollusk;  because  the  shell  was 
primarily  of  use  to  the  mollusk  itself,  and,  so  far  as  the 
mollusk  is  concerned,  the  fact  of  its  shell  being  after- 
wards of  a  secondary  use  to  the  crab  is  quite  immaterial. 
What  Darwin's  challenge  requires  is,  that  some  structure 
or  instinct  should  be  shown  which  is  not  merely  of  such 
secondary  or  accidental  benefit  to  another  species,  but 
clearly  adapted  to  the  needs  of  that  other  species  in  the 
first  instance — such,  for  example,  as  would  be  the  case 
if  the  tail  of  a  rattle-snake  were  of  no  use  to  its 
possessor,  while  serving  to  warn  other  animals  of  the 
proximity  of  a  dangerous  creature  ;  or,  in  the  case  of 
instincts,  if  it  were  true  that  a  pilot-fish  accompanies  a 
shark  for  the  purpose  of  helping  the  shark  to  discover 
food.  Both  these  instances  have  been  alleged  ;  but 
both  have  been  shown  untenable.  And  so  it  has 
proved  of  all  the  other  cases  which  thus  far  have  been 
put  forward. 

Perhaps  the  most  remarkable  of  all  the  allegations 
which  ever  have  been  put  forward  in  this  connexion 
are  those  that  were  current  with  regard  to  instincts 
before  the  publication  of  Darwin's  work.  These 
allegations  are  the  most  remarkable,  because  they 
serve  to  show,  in  a  degree  which  I  do  not  believe 
could  be  shown  anywhere  else,  the  warping  power 
of  preconceived  ideas.  A  short  time  ago  I  happened 
to  come  across  the  8th  edition  of  the  Encyclopedia 
Britannica,  and  turned  up  the  article  on  "  Instinct " 
there,  in  order  to  see  what  amount  of  change  had  been 
wrought  with  regard  to  our  views  on  this  subject  by 
the  work  of  Darwin— the  8th  edition  of  the  Encyclo- 
paedia Britannica  having  been  published  shortly  before 
The  Origin  of  Species  by  means  of  Natural  Selection. 

*  U 


290          Darwin,  and  after  Darwin. 

I  cannot  wait  to  give  any  lengthy  quotations  from 
this  representative  exponent  of  scientific  opinion  upon 
the  subject  at  that  time  ;  but  its  general  drift  may  be 
appreciated  if  I  transcribe  merely  the  short  concluding 
paragraph,  wherein  he  sums  up  his  general  results. 
Here  he  says  : — 

It  thus  only  remains  for  us  to  regard  instinct  as  a  mental 
faculty,  sui  generis,  the  gift  of  God  to  the  lower  animals,  that 
man  in  his  own  person,  and  by  them,  might  be  relieved  from  the 
meanest  drudgery  of  nature. 

Now,  here  we  have  the  most  extraordinary  illus- 
tration that  is  imaginable  of  the  obscuring  influence 
of  a  preconceived  idea.  Because  he  started  with  the 
belief  that  instincts  must  have  been  implanted  in 
animals  for  the  benefit  of  man,  this  writer,  even  when 
writing  a  purely  scientific  essay,  was  completely 
blinded  to  the  largest,  the  most  obvious,  and  the  most 
important  of  the  facts  which  the  phenomena  of  instinct 
display.  For,  as  a  matter  of  fact,  among  all  the  many 
thousands  of  instincts  which  are  known  to  occur  in 
animals,  there  is  no  single  one  that  can  be  pointed  to 
as  having  any  special  reference  to  man  ;  while,  on  the 
other  hand,  it  is  equally  impossible  to  point  to  one 
which  does  not  refer  to  the  welfare  of  the  animal 
presenting  it.  Indeed,  when  the  point  is  suggested, 
it  seems  to  me  surprising  how  few  in  number  are  the 
instincts  of  animals  which  have  proved  to  be  so  much 
as  of  secondary  or  accidental  benefit  to  man,  in  the 
same  way  as  skins,  furs,  and  a  whole  host  of  other 
animal  products  are  thus  of  secondary  use  to  him. 
Therefore,  this  writer  not  only  failed  to  perceive  the 
most  obvious  truth  that  every  instinct,  without  any 
single  exception,  has  reference  to  the  animal  which 


Evidences  of  Theory  of  Natural  Selection.  291 

presents  it ;  but  he  also  conceived  a  purely  fictitious 
inversion  of  this  truth,  and  wrote  an  essay  to  prove  a 
statement  which  all  the  instincts  in  the  animal  kingdom 
unite  in  contradicting. 

This  example  will  serve  to  show,  in  a  striking 
manner,  not  only  the  distance  that  we  have  travelled 
in  our  interpretation  of  organic  nature  between  two 
successive  editions  of  the  Encyclopcedia  Britannica^  but 
also  the  amount  of  verification  which  this  fact  furnishes 
to  the  theory  of  natural  selection.  For,  inasmuch 
as  it  belongs  to  the  very  essence  of  this  theory  that  all 
adaptive  characters  (whether  instinctive  or  structural) 
must  have  reference  to  their  own  possessors,  we  find 
overpowering  verification  furnished  to  the  theory  by 
the  fact  now  before  us — namely,  that  immediately  prior 
to  the  enunciation  of  this  theory,  the  truth  that  all 
adaptive  characters  have  reference  only  to  the  species 
which  present  them  was  not  perceived.  In  other 
words,  it  was  the  testing  of  this  theory  by  the  facts 
of  nature  that  revealed  to  naturalists  the  general  law 
which  the  theory,  as  it  were,  predicted — the  general 
law  that  all  adaptive  characters  have  primary  reference 
to  the  species  which  present  them.  And  when  we 
remember  that  this  is  a  kind  of  verification  which  is 
furnished  by  millions  of  separate  cases,  the  whole 
mass  of  it  taken  together  is,  as  I  have  before  said, 
overwhelming. 

It  is  somewhat  remarkable  that  the  enormous  im- 
portance of  this  argument  in  favour  of  natural 
selection  as  a  prime  factor  of  organic  evolution  has 
not  received  the  attention  which  it  deserves.  Even 
Darwin  himself,  with  his  characteristic  reserve,  has 
not  presented  its  incalculable  significance ;  nor  do  I 
U  2 


29 2          Darwin,  and  after  Darwin. 

know  any  of  his  followers  who  have  made  any  ap- 
proach to  an  adequate  use  of  it  in  their  advocacy 
of  his  views.  In  preparing  the  present  chapter, 
therefore,  I  have  been  particularly  careful  not  to  pitch 
too  high  my  own  estimate  of  its  evidential  value. 
That  is  to  say,  I  have  considered,  both  in  the  domain 
of  structures  and  of  instincts,  what  instances  admit  of 
being  possibly  adduced  per  contra,  or  as  standing  out- 
side the  general  law  that  adaptive  structures  and 
instincts  are  of  primary  use  only  to  their  possessors. 
In  the  result  I  can  only  think  of  two  such  instances. 
These,  therefore,  I  will  now  dispose  of. 

The  first  was  pointed  out,  and  has  been  fully  dis- 
cussed, by  Darwin  himself.  Certain  species  of  ants 
are  fond  of  a  sweet  fluid  that  is  secreted  by  aphides, 
and  they  even  keep  the  aphides  as  we  keep  cows  for 
the  purpose  of  profiting  by  their  "milk."  Now  the 
point  is,  that  the  use  of  this  sweet  secretion  to  the 
aphis  itself  has  not  yet  been  made  out.  Of  course,  if 
it  is  of  no  use  to  the  aphis,  it  would  furnish  a  case 
which  completely  meets  Darwin's  own  challenge.  But, 
even  if  this  supposition  did  not  stand  out  of  analogy 
with  all  the  other  facts  of  organic  nature,  most  of  us 
would  probably  deem  it  prudent  to  hold  that  the 
secretion  must  primarily  be  of  some  use  to  the  aphis 
itself,  although  the  matter  has  not  been  sufficiently 
investigated  to  inform  us  of  what  this  use  is.  For,  in 
any  case,  the  secretion  is  not  of  any  vital  importance 
to  the  ants  which  feed  upon  it :  and  I  think  but  few 
impartial  minds  would  go  so  far  to  save  an  hypothesis 
as  to  maintain,  that  the  Divinity  had  imposed  this  drain 
upon  the  internal  resources  of  one  species  of  insect 
for  the  sole  purpose  of  supplying  a  luxury  to  another. 


Evidences  of  Theory  of  Natural  Selection.  293 

On  the  whole,  it  seems  most  probable  that  the  fluid 
is  of  the  nature  of  an  excretion,  serving  to  carry  off 
waste  products.  Such,  at  all  events,  was  the  opinion 
at  which  Darwin  himself  arrived,  as  a  result  of  ob- 
serving the  facts  anew,  and  in  relation  to  his  theory. 

The  other  instance  to  which  I  have  alluded  as 
seeming  at  first  sight  likely  to  answer  Darwin's 
challenge  is  the  formation  of  vegetable  galls.  The 
great  number  and  variety  of  galls  agree  in  presenting 
a  more  or  less  elaborate  structure,  which  is  not  only 
foreign  to  any  of  the  uses  of  plant-life,  but  singularly 
and  specially  adapted  to  those  of  the  insect-life  which 
they  shelter.  Yet  they  are  produced  by  a  growth  of 
the  plant  itself,  when  suitably  stimulated  by  the 
insects'  inoculation — or,  according  to  recent  observa- 
tions, by  emanations  from  the  bodies  of  the  larvae 
which  develop  from  the  eggs  deposited  in  the  plant 
by  the  insect.  Now,  without  question,  this  is  a  most 
remarkable  fact ;  and  if  there  were  many  more  of  the 
like  kind  to  be  met  with  in  organic  nature,  we  might 
seriously  consider  whether  the  formation  of  galls  should 
not  be  held  to  make  against  the  ubiquitous  agency  of 
natural  selection.  But  inasmuch  as  the  formation  of 
galls  stands  out  as  an  exception  to  the  otherwise 
universal  rule  of  every  species  for  itself,  and  for  itself 
alone,  we  are  justified  in  regarding  this  one  apparent 
exception  with  extreme  suspicion.  Indeed,  I  think 
we  are  justified  in  regarding  the  peculiar  pathological 
effect  produced  in  the  plant  by  the  secretions  of  the 
insect  as  having  been  in  the  first  instance  accidentally 
beneficial  to  the  insects.  Thus,  if  any  other  effect 
than  that  of  a  growing  tumour  had  been  produced  in 


294          Darwin,  and  after  Darwin. 

the  first  instance,  or  if  the  needs  of  the  insect  progeny 
had  not  been  such  as  to  have  derived  profit  from 
being  enclosed  in  such  a  tumour,  then,  of  course,  the 
inoculating  instinct  of  these  animals  could  not  have 
been  developed  by  natural  selection.  But  given  these 
two  conditions,  and  it  appears  to  me  there  is  nothing 
very  much  more  remarkable  about  an  accidental 
correlation  between  the  effects  of  a  parasitic  larva  on 
a  plant  and  the  needs  of  that  parasite,  than  there  is 
between  the  similarly  accidental  correlation  between 
a  hydated  parasite  and  the  nutrition  furnished  to  it  by 
the  tissues  of  a  warm-blooded  animal.  Doubtless  the 
case  of  galls  is  somewhat  more  remarkable,  inasmuch 
as  the  morbid  growth  of  the  plant  has  more  concern 
in  the  correlation — being,  in  many  instances,  a  more 
specialized  structure  on  the  part  of  a  host  than  occurs 
anywhere  else,  either  in  the  animal  or  vegetable  world. 
But  here  I  may  suggest  that  although  natural  selection 
cannot  have  acted  upon  the  plant  directly,  so  as  to  have 
produced  galls  ever  better  and  better  adapted  to  the 
needs  of  the  insect,  it  may  have  so  acted  upon  the 
plants  indirectly  through  the  insects.  For  it  may  very 
well  have  been  that  natural  selection  would  ever 
tend  to  preserve  those  individual  insects,  the  quality 
of  whose  emanations  tended  to  produce  the  form  of  galls 
best  suited  to  nourish  the  insect  progeny  ;  and  thus 
the  character  of  these  pathological  growths  may  have 
become  ever  better  and  better  adapted  to  the  needs 
of  the  insects.  Lastly,  looking  to  the  enormous 
number  of  relations  and  inter-relations  between  all 
organic  species,  it  is  scarcely  to  be  wondered  at  that 
even  so  extraordinary  an  instance  of  correlation  as 
this  should  have  arisen  thus  by  accident,  and  then 


Evidences  of  Theory  of  'Natural  Selection.  295 

have  been  perfected  by  such  an  indirect  agency  of 
natural  selection  as  is  here  suggested x. 

The  third  general  class  of  facts  which  tell  so  im- 
mensely in  favour  of  natural  selection  as  an  important 
cause  of  organic  evolution,  are  those  of  domestication. 
The  art  of  the  horticulturist,  the  fancier,  the  cattle- 
breeder,  &c.,  consists  in  producing  greater  and  greater 
deviations  from  a  given  wild  type  of  plant  or  animal, 
in  any  particular  direction  that  may  be  desired  for 
purposes  either  of  use  or  of  beauty.  Cultivated 
cereals,  fruits,  and  flowers  are  known  to  have  been 
all  derived  from  wild  species  ;  and,  of  course,  the  same 
applies  to  all  our  domesticated  varieties  of  animals. 
Yet  if  we  compare  a  cabbage  rose  with  a  wild  rose,  a 
golden  pippin  apple  with  a  crab,  a  toy  terrier  with  any 
species  of  wild  dog,  not  to  mention  any  number  of  other 
instances,  there  can  be  no  question  that,  if  such  differ- 
ences had  appeared  in  nature,  the  organisms  presenting 
them  would  have  been  entitled  to  rank  as  distinct 
species — or  even,  in  many  cases,  as  distinct  genera. 
Yet  we  know,  as  a  matter  of  fact,  that  all  these 
differences  have  been  produced  by  a  process  of  arti- 
ficial selection,  or  pairing,  which  has  been  continuously 
practised  by  horticulturists  and  breeders  through  a 
number  of  generations.  It  is  the  business  of  these  men 
to  note  the  individual  organisms  which  show  most 
variation  in  the  directions  required,  and  then  to 
propagate  from  these  individuals,  in  order  that  the 
progeny  shall  inherit  the  qualities  desired.  The 
results  thus  become  cumulative  from  generation  to 
generation,  until  we  now  have  an  astonishing  mani- 
1  Note  B. 


296          Darwin,  and  after  Darwin • 

festation  of  useful  qualities  on  the  one  hand,  and  of 
beautiful  qualities  on  the  other,  according  as  the 
organisms  have  been  thus  bred  for  purposes  of  use  or 
for  those  of  beauty. 

Now  it  is  immediately  obvious  that  in  these  cases 
the  process  of  artificial  selection  is  precisely  analogous 
to  that  of  natural  selection  (and  of  sexual  selection 
which  will  be  considered  later  on),  in  all  respects  save 
one  :  the  utility  or  the  beauty  which  it  is  the  aim  of 
artificial  selection  continually  to  enhance,  is  utility  or 
beauty  in  relation  to  the  requirements  or  to  the  tastes 
of  man  ;  whereas  the  utility  or  the  beauty  which  is 
produced  by  natural  selection  and  sexual  selection  has 
reference  only  to  the  requirements  or  the  tastes  of 
the  organisms  themselves.  But,  with  the  exception 
of  this  one  point  of  difference,  the  processes  and  the 
products  are  identical  in  kind.  Persevering  selection 
by  man  is  thus  proved  to  be  capable  of  creating  what 
are  virtually  new  specific  types,  and  this  in  any 
required  direction.  Hence,  when  we  remember  how 
severe  is  the  struggle  for  existence  in  nature,  it 
becomes  impossible  to  doubt  that  selection  by  nature 
is  able  to  do  at  least  as  much  as  artificial  selection  in 
the  way  of  thus  creating  new  types  out  of  old  ones. 
Artificial  selection,  indeed,  notwithstanding  the  many 
and  marvellous  results  which  it  has  accomplished,  can 
only  be  regarded  as  but  a  feeble  imitation  of  natural 
selection,  which  must  act  with  so  much  greater 
vigilance  and  through  such  immensely  greater  periods 
of  time.  In  a  word,  the  proved  capabilities  of  arti- 
ficial selection  furnish,  in  its  best  conceivable  form, 
what  is  called  an  argument  a  fortiori  in  favour  of 
natural  selection. 


Evidences  of  Theory  of  Natural  Selection.  297 

Or,  to  put  it  in  another  way,  it  may  be  said  that 
for  thousands  of  years  mankind  has  been  engaged  in 
making  a  gigantic  experiment  to  test,  as  it  were  by 
anticipation,  the  theory  of  natural  selection.  For, 
although  this  prolonged  experiment  has  been  carried 
on  without  any  such  intention  on  the  part  of  the  ex- 
perimenters, it  is  none  the  less  an  experiment  in  the 
sense  that  its  results  now  furnish  an  overwhelming 
verification  of  Mr.  Darwin's  theory.  That  is  to  say, 
they  furnish  overwhelming  proof  of  the  efficacy  of  the 
selective  principle  in  the  modification  of  organic  types, 
when  once  this  principle  is  brought  steadily  and  con- 
tinuously to  bear  upon  a  sufficiently  long  series  of 
generations. 

In  order  to  furnish  ocular  evidence  of  the  value  of 
this  line  of  verification,  I  have  had  the  following  series 
of  drawings  prepared.  Another  and  equally  striking 
series  might  be  made  of  the  products  of  artificial 
selection  in  the  case  of  plants ;  but  it  seems  to  me 
that  the  case  of  animals  is  more  than  sufficient  for  the 
purpose  just  stated.  Perhaps  it  is  desirable  to  add 
that  considerable  care  has  been  bestowed  upon  the 
execution  of  these  portraits  ;  and  that  in  every  case 
the  latter  have  been  taken  from  the  most  typical 
specimens  of  the  artificial  variety  depicted.  Those  of 
them  which  have  not  been  drawn  directly  from  life 
are  taken  from  the  most  authoritative  sources  ;  and, 
before  being  submitted  to  the  engraver,  they  were  all 
examined  by  the  best  judges  in  each  department  In 
none  of  the  groups,  however,  have  I  aimed  at  an 
exhaustive  representation  of  all  the  varieties :  I 
have  merely  introduced  representatives  of  as  many 
as  the  page  would  in  each  case  accommodate. 


1 

FIG.  91. — Pigeons.     Drawn  from  life  (prize  specimens). 


FlG.  92.— Pigeons,  continued.     Drawn  from  life  (prize  specimens). 


FIG.  93. — Fowls.     Drawn  from  life  (prize  specimens). 


FIG  94  -Fowls,  continued.     Drawn  from  life  (prize  specimens). 


FlG.  95. — Pair  of  Japanese  Fowls,  lot 
in  the 


j-tailed  breed.   Drawn  from  stuffed  specimens 
(ritish  Museum. 


FIG  96.-  Canaries.     Drawn  from  life  (prize  specimens). 


FIG.  97.— Sebastopol,  or  Frizzled  Goose.     Drawn  from  a  photograph 


FIG.  98.— The  Dingo,  or  wild  dog  of  Australia,  ^  nat.  size.    Drawn  from  life. 
(Zoological  Gat  den s). 


FIG.  99.— Dogs.     Drawn  from  life  (piize  specimens). 

X 


FlG.  loo.  — Dogs,  coiil.uurJ.     Drawn  from  lik-  (prize  specimens) 


FlG    ioi.— The  Hairless  Dog  of  Japan,  ,'„  nat.  size.     Drawn  from  a  photogiaph, 
kindly  lent  for  the  purpose  by  the  proprietor. 


DEEK 


FlG.  iu2.—  The  skull  of  a  Hull-dog  compared  with  that  oi  a  Decrliouud.     Drawn 
frojii  natura. 

X    2 


ViLjb  fypP  7T. 
FlG.  103.     Rabbits.     Drawn  from  lile  (prize  specimens). 


SHIRE  HORSE. 

"pR,itJc£.  WILLIAM 


FlG.  104.- Horses.     Drawn  from  life  (prize  specimens). 


FlG.  105.- Sheep.     The  illustrations  are  confined  to  British  breeds.     Drawu  from 
lile  (prize  specimens). 


FIG.  106  --Cattle.     The  illustrations  are  confined  to  British  breeds.     Drawn  from 
life  (prize  specimens). 


312  Darwin,  and  after  Darwin. 


FIG.   107. — Wild  Boar  contrasted   with  a  modern  Domesticated  Pig. 
Drawn  from  life  {Zoological  Gardens,  and  prize  specimen). 

The  exigencies  of  space  have  prevented,  in  some  of 
the  groups,  strict  adherence  to  a  uniform  scale — with 
the  result  that  contrasts  between  different  breeds  in 
respect  of  size  are  not  adequately  rendered.  This 
remark  applies  especially  to  the  dogs  ;  for  although 
the  artist  has  endeavoured  to  draw  them  in  perspective, 
unless  the  distance  between  those  in  the  foreground 
and  those  in  the  background  is  understood  to  be 
more  considerable  than  it  appears,  an  inadequate  idea 
is  given  of  the  relative  differences  of  size.  The  most 
instructive  of  the  groups,  I  think,  is  that  of  the 
Canaries  ;  because  the  many  and  great  changes  in 


Evidences  of  Theory  of  Natural  Selection.  313 

different  directions  must  in  this  case  have  been 
produced  by  artificial  selection  in  so  comparatively 
short  a  time — the  first  mention  of  this  bird  that  I  can 
find  being  by  Gesner,  in  the  sixteenth  century. 

Now,  it  is  surely  unquestionable  that  in  these 
typical  proofs  of  the  efficacy  of  artificial  selection  in 
the  modification  of  specific  types,  we  have  the  strongest 
conceivable  testimony  to  the  power  of  natural  selection 
in  the  same  direction.  For  it  thus  appears  that 
wherever  mankind  has  had  occasion  to  operate  by 
selection  for  a  sufficiently  long  time — that  is  to  say,  on 
whatever  species  of  plant  or  animal  he  chooses  thus  to 
operate  for  the  purpose  of  modifying  the  type  in  any 
required  direction, — the  results  are  always  more  or  less 
the  same  :  he  finds  that  all  specific  types  lend  them- 
selves to  continuous  deflection  in  any  particulars  of 
structure,  colour,  &c.,  that  he  may  desire  to  modify. 

Nevertheless,  to  this  parallel  between  the  known 
effects  of  artificial  selection,  and  the  inferred  effects  of 
natural  selection,  two  objections  have  been  urged. 
The  first  is,  that  in  the  case  of  artificial  selection  the 
selecting  agent  is  a  voluntary  intelligence,  while  in  the 
case  of  natural  selection  the  selecting  agent  is  Nature 
herself ;  and  whether  or  not  there  is  any  counterpart 
of  man's  voluntary  intelligence  in  nature  is  a  question 
with  which  Darwinism  has  nothing  to  do.  Therefore, 
it  is  alleged,  the  analogy  between  natural  selection 
and  artificial  selection  fails  ab  initio,  or  at  the  fountain- 
head  of  the  causes  which  are  taken  by  the  analogy  to 
be  respectively  involved. 

The  second  objection  to  the  analogy  is,  that  the 
products  of  artificial  selection,  closely  as  they  may 


314          Darwin,  and  after  Darwin. 

resemble  natural  species  in  all  other  respects,  never- 
theless present  one  conspicuous  and  highly  important 
point  of  difference :  they  rarely,  if  ever,  present  the 
physiological  character  of  mutual  infertility,  which  is 
a  character  of  extremely  general  occurrence  in  the 
case  of  natural  species,  even  when  these  are  most 
nearly  allied. 

I  will  deal  with  these  two  objections  in  the  next 
chapter,  where  I  shall  be  concerned  with  the  meeting 
of  all  the  objections  which  have  ever  been  urged 
against  the  theory  of  natural  selection.  Meanwhile  I 
am  engaged  only  in  presenting  the  general  arguments 
which  support  the  theory,  and  therefore  mention  these 
objections  to  one  of  them  merely  en  passant.  And  I 
do  so  in  order  to  pledge  myself  effectually  to  dispose 
of  them  later  on,  so  that  for  the  purposes  of  my  present 
argument  both  these  objections  may  be  provisionally 
regarded  as  non-existent;  which  means,  in  other 
words,  that  we  may  provisionally  regard  the  analogy 
between  artificial  selection  and  natural  selection  as 
everywhere  logically  intact 

To  sum  up,  then,  the  results  of  the  foregoing 
exposition  thus  far,  what  I  hold  to  be  the  three 
principal,  or  most  general,  arguments  in  favour  of  the 
•:heory  of  natural  selection,  are  as  follows. 

First,  there  is  the  a  priori  consideration  that,  if  on 
independent  grounds  we  believe  in  the  theory  of 
evolution  at  all,  it  becomes  obvious  that  natural 
selection  must  have  had  some  part  in  the  process. 
For  no  one  can  deny  the  potent  facts  of  heredity, 
variability,  the  struggle  for  existence,  and  survival  of 
the  fittest.  But  to  admit  these  facts  is  to  admit 


Evidences  of  Theory  of  Natural  Selection.  3 1 5 

natural  selection  as  a  principle  which  must  be,  at  any 
rate,  one  of  the  factors  of  organic  evolution,  supposing 
such  evolution  to  have  taken  place.  Next,  when  we 
turn  from  these  a  priori  considerations,  which  thus 
show  that  natural  selection  must  have  been  concerned 
to  some  extent  in  the  process  of  evolution,  we  find  in 
organic  nature  evidence  a  posteriori  of  the  extent  to 
which  this  principle  has  been  thus  concerned.  For  we 
find  that  among  all  the  countless  millions  oi  adaptive 
structures  which  are  to  be  met  with  in  organic  nature, 
it  is  an  invariable  rule  that  they  exist  in  relation  to  the 
needs  of  the  particular  species  which  present  them : 
they  never  have  any  primary  reference  to  the  needs  of 
other  species.  And  as  this  extraordinarily  large  and 
general  fact  is  exactly  what  the  theory  of  natural 
selection  would  expect,  the  theory  is  verified  by  the 
fact  in  an  extraordinarily  cogent  manner.  In  other 
words,  the  fact  goes  to  prove  that  in  all  cases  where 
adaptive  structures  or  instincts  are  concerned,  natural 
selection  must  have  been  either  the  sole  cause  at  work, 
or,  at  the  least,  an  influence  controlling  the  operation 
of  all  other  causes. 

Lastly,  an  actually  experimental  verification  of  the 
theory  has  been  furnished  on  a  gigantic  scale  by  the 
operations  of  breeders,  fanciers,  and  horticulturists. 
For  these  men,  by  their  process  of  selective  accumula- 
tion, have  empirically  proved  what  immense  changes 
of  type  may  thus  be  brought  about;  and  so  have 
verified  by  anticipation,  and  in  a  most  striking  man- 
ner, the  theory  of  natural  selection — which,  as  now 
so  fully  explained,  is  nothing  more  than  a  theory 
of  cumulative  modifications  by  means  of  selective 
breeding. 


316          Darwin,  and  after  Darwin. 

So  much,  then,  by  way  of  generalities.  But  perhaps 
the  proof  of  natural  selection  as  an  agency  of  the  first 
importance  in  the  transmutation  of  species  may  be  best 
brought  home  to  us  by  considering  a  few  of  its 
applications  in  detail.  I  will  therefore  devote  the  rest 
of  the  present  chapter  to  considering  a  few  cases  of  this 
kind. 

There  are  so  many  large  fields  from  which  such 
special  illustrations  may  be  supplied,  that  it  is  difficult 
to  decide  which  of  them  to  draw  upon.  For  instance, 
the  innumerable  always  interesting,  and  often  aston- 
ishing adaptations  on  the  part  of  flowers  to  the 
fertilising  agency  of  insects,  has  alone  given  rise  to  an 
extensive  literature  since  the  time  when  Darwin  him- 
self was  led  to  investigate  the  subject  by  the  guidance 
of  his  own  theory.  The  same  may  be  said  of  the 
structures  and  movements  of  climbing  plants,  and,  in 
short,  of  all  the  other  departments  of  natural  history 
where  the  theory  of  natural  selection  has  led  to  the 
study  of  the  phenomena  of  adaptation.  For  in  all  these 
cases  the  theory  of  natural  selection,  which  first  led  to 
their  discovery,  still  remains  the  only  scientific  theory 
by  which  they  can  be  explained.  But  among  all  the 
possible  fields  from  which  evidences  of  this  kind  may 
be  drawn,  I  think  the  best  is  that  which  may  be 
generically  termed  defensive  colouring.  To  this  field, 
therefore,  I  will  restrict  myself.  But,  even  so,  the 
cases  to  be  mentioned  are  but  mere  samples  taken 
from  different  divisions  of  this  field  ;  and  therefore  it 
must  be  understood  at  the  outset  that  they  could 
easily  be  multiplied  a  hundred-iold. 


Evidences  of  Theory  of  Natural  Selection.  3  j  7 

Protective  Colouring. 

A  vast  number  of  animals  are  rendered  more  or  less 
inconspicuous  by  resembling  the  colours  of  the  surfaces 
on  which  they  habitually  rest.  Such,  for  example, 
are  grouse,  partridges,  rabbits,  &c.  Moreover,  there 


IB 


FIG.  108.— Sen  son  nl  changes  of  colour  in  Ptarmigan  (Lagofus  mutus). 
Drawn  from  stuffed  specimens  in  the  British  Museum,  ^  nat.  size, 
with  appropriate  surroundings  supplied. 

are  many  cases  in  which,  if  the  needs  of  the  creature 
be  such  that  it  must  habitually  frequent  surfaces  of 
different  colours,  it  has  acquired  the  power  of  changing 
its  colour  accordingly — e.  g.  cuttle-fish,  flat-fish, 
frogs,  chameleons,  &c.  The  physiological  mechanism 
whereby  these  adaptive  changes  of  colour  are  pro- 


318  Darwin,  and  after  Darwin. 

duced  differs  in  different  animals;  but  it  is  needless 
for  our  purposes  to  go  into  this  part  of  the  subject. 
Again,  there  are  yet  other  cases  where  protective 
colouring  which  is  admirably  suited  to  conceal  an 
animal  through  one  part  of  the  year,  would  become 
highly  conspicuous  during  another  part  of  it—  namely, 
when  the  ground  is  covered  with  snow.  Accordingly, 
in  these  cases  the  animals  change  their  colour  in  the 
winter  months  to  a  snowy  white :  witness  stoats, 
mountain  hares,  ptarmigan,  &c.  (Fig.  108.) 

Now,  it  is  sufficiently  obvious  that  in  all  these 
classes  of  cases  the  concealment  from  enemies  or 
prey  which  is  thus  secured  is  of  advantage  to  the 
animals  concerned  ;  and,  therefore,  that  in  the  theory 
of  natural  selection  we  have  a  satisfactory  theory 
whereby  to  explain  it.  And  this  cannot  be  said  of 
any  other  theory  of  adaptive  mechanisms  in  nature 
that  has  ever  been  propounded.  The  so-called  La- 
marckian  theory,  for  instance,  cannot  be  brought  to 
bear  upon  the  facts  at  all  ;  and  on  the  theory  of 
special  creation  it  is  unintelligible  why  the  phenomena 
of  protective  colouring  should  be  of  such  general 
occurrence.  For,  in  as  far  as  protective  colouring 
is  of  advantage  to  the  species  which  present  it,  it  is 
of  corresponding  disadvantage  to  thoje  other  species 
against  the  predatory  nature  of  which  it  acts  as  a 
defence  And,  of  course,  the  same  applies  to  yet 
other  species,  if  they  serve  as  prey.  Moreover,  the 
more  minutely  this  subject  is  investigated  in  all  its 
details,  the  more  exactly  is  it  found  to  harmonise 
with  the  naturalistic  interpretation  1. 

1  Were  it  not  that  some  of  Darwin's  critics  have  overlooked  the  very 
point  wherein  the  great  value  of  protective  colouring  as  evidence  of 


Evidences  of  Theory  of  Natural  Selection.  319 

In  the  first  place,  we  always  find  a  complete  cor- 
respondence between  imitative  colouring  and  instinctive 
endowment.  If  a  caterpillar  exactly  resembles  the 
colour  of  a  twig,  it  also  presents  the  instinct  of 
habitually  reposing  in  the  attitude  which  makes  it 
most  resemble  a  twig — standing  out  from  the  branch 
on  which  it  rests  at  the  same  angle  as  is  presented 
by  the  real  twigs  of  the  tree  on  which  it  lives. 

Here,  again,  is  a  bird  protectively  coloured  so  as  to 
resemble  stones  upon  the  rough  ground  where  it 
habitually  lives  ;  and  the  drawing  shows  the  attitude 
in  which  the  bird  instinctively  reposes,  so  as  still  further 
to  increase  its  resemblance  to  a  stone.  (Fig.  109.) 

To  take  only  one  other  instance,  hares  and  rabbits, 
like  grouse  and  partridges — or  like  the  plover  just 
alluded  to, — instinctively  crouch  upon  those  surfaces 
the  colours  of  which  they  resemble  ;  and  I  have  often 
remarked  that  if,  on  account  of  any  individual 
peculiarity  of  coloration,  the  animal  is  not  able  thus 

natural  selection  consists,  it  would  be  needless  to  observe  that  it  does  so 
in  the  minuteness  of  the  protective  resemblance  which  in  so  many 
cases  is  presented.  Of  course  where  the  resemblance  is  only  very  general, 
the  phenomena  might  be  ascribed  to  mere  coincidence,  of  which  the 
instincts  of  the  animal  have  taken  advantage.  But  in  the  measure 
that  the  resemblance  becomes  minutely  detailed,  the  supposition 
of  mere  coincidence  is  excluded,  and  the  agency  of  some  specially 
adaptive  cause  demonstrated.  Again,  it  is  almost  needless  to  say,  no  real 
difficulty  is  presented  (as  has  been  alleged)  by  the  cases  above  quoted  of 
seasonal  imitations,  on  the  ground  that  natural  selection  could  not  act 
alternately  on  the  same  individual.  Natural  selection  is  not  supposed  to 
act  alternately  on  the  same  individual.  It  is  supposed  to  act  always  in 
the  same  manner,  and  if,  as  in  the  case  of  a  regularly  recurring  change 
in  the  colours  of  the  environment,  correspondingly  recurrent  changes  are 
icquired  to  appear  in  the  colours  of  the  animals,  natural  selection  sets 
its  premium  upon  those  individuals  the  constitutions  of  which  best  lend 
themselves  to  seasonal  changes  of  the  needful  kind — probably  under  the 
influence  of  stimuli  supplied  by  the  changes  of  external  conditions 
(temperature,  moisture,  &c.). 


320          Darwin,  and  after  Darwin. 

to  secure  concealment,  it  nevertheless  exhibits  the 
instinct  of  crouching  which  is  of  benefit  to  all  its 
kind,  although,  from  the  accident  of  its  own  abnormal 
colouring,  this  instinct  is  then  actually  detrimental 
to  the  animal  itself.  For  example,  every  sportsman 


" 

..,,,  f^,,^_ 


YlG.  109. —  CEdicnemus  crepitans,  showing  the  instinctive  attitude  of 
concealment.  Drawn  from  a  stuffed  specimen  in  the  British  Museum, 
J  nat.  size,  with  appropriate  surroundings  supplied. 

must  have  noticed  that  the  somewhat  rare  melanic 
variety  of  the  common  rabbit  will  crouch  as  steadily 
as  the  normal  brownish-gray  type,  notwithstanding 
that,  owing  to  its  abnormal  colour,  a  "  nigger-rabbit  " 
thus  renders  itself  the  most  conspicuous  object  in  the 


Evidences  of  Theory  of  Natural  Selection.  3  2 1 

landscape.  In  all  such  cases,  of  course,  there  has 
been  a  deviation  from  the  normal  type  in  respect 
of  colour,  with  the  result  that  the  inherited  instinct 
is  no  longer  in  tune  with  the  other  endowments  of 
the  animal.  Such  a  variation  of  colour,  therefore, 
will  tend  to  be  suppressed  by  natural  selection  ;  while 
any  variations  which  may  bring  the  animal  still  more 
closely  to  resemble  its  habitual  surroundings  will  be 
preserved.  Thus  we  can  understand  the  truly 
wonderful  extent  to  which  this  principle  of  protective 
colouring  has  been  carried  in  many  cases  where  the 
need  of  it  has  been  most  urgent. 

Not  only  colour,  but  structure,  may  be  profoundly 
modified  for  the  purposes  of  protective  concealment. 
Thus,  caterpillars  which  resemble  twigs  do  so  not 
only  in  respect  of  colour,  but  also  of  shape ;  and  this 
even  down  to  the  most  minute  details  in  cases  where 
the  adaptation  is  most  complete  :  certain  butterflies 
and  leaf-insects  so  precisely  resemble  the  leaves  upon 
which,  or  among  which,  they  live,  that  it  is  almost 
impossible  to  detect  them  in  the  foliage — not  only 
the  colour,  the  shape,  and  the  venation  being  all 
exactly  imitated,  but  in  some  cases  even  the  defects 
to  which  the  leaves  are  liable,  in  the  way  of  fungoid 
growths,  &c.  There  are  other  insects  which  with 
similar  exactness  resemble  moss,  lichens,  and  so  forth. 
A  species  of  fish  secures  a  complete  resemblance  to 
bunches  of  sea-weed  by  a  frond-like  modification 
of  all  its  appendages,  and  so  on  through  many  other 
instances.  Now,  in  all  such  cases  where  there  is  so 
precise  an  imitation,  both  in  colour  and  structure, 
it  seems  impossible  to  suggest  any  other  explana- 
tion of  the  facts  than  the  one  which  is  supplied  by 

*  Y 


FIG.  no.— Imitative  forms  and  colours  in  insects.     Drawn  from  nature  (^    Coll 
Surf.  Mus.). 


Evidences  of  Theory  of  Natural  Selection.  323 

Mr.  Darwin's  theory — namely,  that  the  more  perfect 
the  resemblance  is  caused  to  become  through  the 
continuous  influence  of  natural  selection  always  picking 
out  the  best  imitations,  the  more  highly  discriminative 
becomes  the  perception  of  those  enemies  against  the 
depredations  of  which  this  peculiar  kind  of  protection 
is  developed  ;  so  that,  in  virtue  of  this  action  and 
re-action,  eventually  we  have  a  degree  of  imitation 
which  renders  it  almost  impossible  for  a  naturalist 
to  detect  the  animal  when  living  in  its  natural  en- 
vironment. 

Warning  Colours. 

In  strange  and  glaring  contrast  to  all  these  cases 
of  protective  colouring,  stand  other  cases  of  conspic- 
uous colouring.  Thus,  for  example,  although  there 
are  numberless  species  of  caterpillars  which  present 
in  an  astonishing  degree  the  phenomena  of  pro- 
tective colouring,  there  are  numberless  other  species 
which  not  only  fail  to  present  these  phenomena  in 
any  degree,  but  actually  go  to  the  opposite  extreme 
of  presenting  colours  which  appear  to  have  been 
developed  for  the  sake  of  their  conspicuousness.  At 
all  events,  these  caterpillars  are  usually  the  most  con- 
spicuous objects  in  their  surroundings,  and  therefore 
in  the  early  days  of  Darwinism  they  were  regarded  by 
Darwin  himself  as  presenting  a  formidable  difficulty 
in  the  way  of  his  theory.  To  Mr.  Wallace  belongs 
the  merit  of  having  cleared  up  this  difficulty  in 
an  extraordinarily  successful  manner.  He  virtually 
reasoned  thus.  If  the  raison  d'etre  of  protective 
colouring  be  that  of  concealing  agreeably  flavoured 
caterpillars  from  the  eye-sight  of  birds,  may  not 
Y  2 


324          Darwin,  and  after  Darwin. 

the  raison  cCfare  of  conspicuous  colouring  be  that 
of  protecting  disagreeably  flavoured  caterpillars 
from  any  possibility  of  being  mistaken  by  birds? 
Should  this  be  the  case,  of  course  the  more  con- 
spicuous the  colouring  the  better  would  it  be  for 
the  caterpillars  presenting  it.  Now  as  soon  as  this 
suggestion  was  acted  upon  experimentally,  it  was 
found  to  be  borne  out  by  facts.  Birds  could  not  be 
induced  to  eat  caterpillars  of  the  kinds  in  question; 
and  there  is  now  no  longer  any  doubt  that  their  con- 
spicuous colouring  is  correlated  with  their  distasteful- 
ness  to  birds,  in  the  same  way  as  the  inconspicuous  or 
imitative  colouring  of  other  caterpillars  is  correlated 
with  their  tastefulness  to  b:rds.  Here  then  is  yet 
another  instance,  added  to  those  already  given,  of 
the  verification  yielded  to  the  theory  of  natural 
selection  by  its  proved  competency  as  a  guide  to  facts 
in  nature ;  for  assuredly  this  particular  class  of  facts 
would  never  have  been  suspected  but  for  its  suggestive 
agency. 

As  in  the  case  of  protective  imitation,  so  in  this 
case  of  warning  conspicuousness,  not  only  colour,  but 
structure  may  be  greatly  modified  for  the  purpose 
of  securing  immunity  from  attack.  Here,  of  course, 
the  object  is  to  assume,  as  far  as  possible,  a  touch- 
me-not  appearance ;  so  that,  although  destitute  of 
any  real  means  of  offence,  the  creatures  in  question 
present  a  fictitiously  dangerous  aspect.  As  the 
Devil's-coach-horse  turns  up  his  stingless  tail  when 
threatened  by  an  enemy,  so  in  numberless  ways  do 
many  harmless  animals  of  all  classes  pretend  to  be 
formidable.  But  the  point  now  is  that  these  instincts 
of  self-defence  are  often  helped  out  by  structural 


Evidences  of  Theory  of  Natural  Selection.  325 

modifications,  expressly  and  exclusively  adapted  to 
this  end.  For  example,  what  a  remarkable  series  of 
protective  adjustments  occurs  in  the  life-history  of  the 
Puss  Moth — culminating  with  so  comical  an  instance 
of  the  particular  device  now  under  consideration  as 
the  following.  I  quote  the  facts  from  Mr.  E.  B. 
Poulton's  admirable  book  on  The  Colours  of  Animals 
(PP  269-271). 

The  larva  of  the  Puss  Moth  (Cerura  vinula)  is  very  common 
upon  poplar  and  willow.  The  circular  dome-like  eggs  are  laid, 
either  singly  or  in  little  groups  of  two  or  three,  upon  the  upper 
side  of  the  leaf,  and  being  of  a  reddish  colour  strongly  suggest 
the  appearance  of  little  galls,  or  the  results  of  some  other  injury 


FlG.   in. — The  larva  of  Puss  Moth  (C.  vinula}  when  undisturbed; 
full-fed ;  natural  size. 

to  the  leaf.  The  youngest  larvag  are  black,  and  also  rest  upon 
the  upper  surface  of  the  leaf,  resembling  the  dark  patches  which 
are  commonly  seen  in  this  position.  As  the  larva  grows,  the 
apparent  black  patch  would  cover  too  large  a  space,  and  would 
lead  to  detection  if  it  still  occupied  the  whole  surface  of  the  body. 
The  latter  gains  a  green  ground-colour  which  harmonises  with 
the  leaf,  while  the  dark  marking  is  chiefly  confined  to  the  back. 
As  growth  proceeds  the  relative  amount  of  green  increases,  and 
the  dark  mark  is  thus  prevented  from  attaining  a  size  which 
would  render  it  too  conspicuous.  In  the  last  stage  of  growth 
the  green  larva  becomes  very  large,  and  usually  rests  on  the 
twigs  of  its  food-plant  (Fig.  1 1 1).  The  dark  colour  is  still  present 
on  the  back  but  is  softened  to  a  purplish  tint,  which  tends  to  be 
replaced  by  a  combination  of  white  and  green  in  many  of  the 
largest  larvae.  Such  a  larva  is  well  concealed  by  General  Pro- 


326          Darwin,  and  after  Darwin. 


tective  Resemblance,  and  one  may  search  a  long  time  before 
finding  it,  although  assured  of  its  presence  from  the  stripped 
branches  of  the  food-plant  and  the  faeces  on  the  ground  beneath. 
As  soon  as  a  large  larva  is  discovered  and  disturbed  it  with- 
draws its  head  into  the  first  body-ring,   inflating  the   margin, 
which  is  of  a  bright  red  colour.     There  are  two  intensely  black 
spots    on    this   margin   in  the 
appropriate  position  for  eyes, 
and  the  whole   appearance  is 
that   of  a  large   flat   face   ex- 
tending to  the   outer  edge   of 
the  red  margin  (see  Fig.  112). 
The  effect  is  an  intensely  ex- 
aggerated caricature  of  a  ver- 
tebrate face,  which  is  probably 
alarming    to     the    vertebrate 
FIG.  i 1 2.— The  larva  of  Puss  Moth    enemies  of  the  caterpillar.  The 
in  its  terrifying  attitude  after  be-  .r  .  ,-,.  ,        c 

ing  disturbed f  full-fed;   natural    ^™*    effeCt    1S    theref°re 
sjZCt  mimetic.     The  movements  en- 

tirely depend  on  tactile  im- 
pressions :  when  touched  ever  so  lightly  a  healthy  larva  im- 
mediately assumes  the  terrifying  attitude,  and  turns  so  as  to 
present  its  full  face  towards  the  enemy  ;  if  touched  on  the 
other  side  or  on  the  back  it  instantly  turns  its  face  in  the  ap- 
propriate direction.  The  effect  is  also  greatly  strengthened  by 
two  pink  whips  which  are  swiftly  protruded  fiom  the  prongs 
of  the  fork  in  which  the  body  terminates.  The  prongs  represent 
the  last  pair  of  larval  legs  which  have  been  greatly  modified 
from  their  ordinary  shape  and  use.  The  end  of  the  body  is  at 
the  same  time  curved  forward  over  the  back  (generally  much 
further  than  in  Fig.  112),  so  that  the  pink  filaments  are  brandished 
above  the  head. 

Mimicry. 

Lastly,  these  facts  as  to  imitative  and  conspicuous 
colouring  lead  on  to  the  yet  more  remarkable  facts  of 
what  is  called  mimicry.  By  mimicry  is  meant  the 
imitation  in  form  and  colour  of  one  species  by  another, 


Evidences  of  Theory  of  Natural  Selection.  327 

in  order  that  the  imitating  species  may  be  mistaken 
for  the  imitated,  and  thus  participate  in  some  ad- 
vantage which  the  latter  enjoys.  For  instance,  if,  as 
in  the  case  of  the  conspicuously-coloured  caterpillars, 
it  is  of  advantage  to  an  ill-savoured  species  that  it 
should  hold  out  a  warning  to  enemies,  clearly  it  may 
be  of  no  less  advantage  to  a  well-savoured  species 
that  it  should  borrow  this  flag,  and  thus  be  mistaken 
for  its  ill-savoured  neighbour.  Now,  the  extent  to 
which  this  device  of  mimicry  is  carried  is  highly  re- 
markable, not  only  in  respect  of  the  number  of  its 
cases,  but  also  in  respect  of  the  astonishing  accuracy 
which  in  most  of  these  cases  is  exhibited  by  the 
imitation.  There  need  be  little  or  virtually  no 
zoological  affinity  between  the  imitating  and  the 
imitated  forms  ;  that  is  to  say,  in  some  cases  the 
zoological  affinity  is  not  closer  than  ordinal,  and 
therefore  cannot  possibly  be  ascribed  to  kinship. 
Like  all  the  other  branches  of  the  general  subject  of 
protective  resemblance  in  form  or  colouring,  this 
branch  has  already  been  so  largely  illustrated  by 
previous  writers,  that,  as  in  the  previous  cases,  I  need 
only  give  one  or  two  examples.  Those  which  I 
choose  are  chosen  on  account  of  the  colours  concerned 
not  being  highly  varied  or  brilliant,  and  therefore 
lending  themselves  to  less  ineffectual  treatment  by 
wood- engraving  than  is  the  case  where  attempts  are 
made  to  render  by  this  means  even  more  remarkable 
instances.  (Figs.  113,  114,  115.) 

It  is  surely  apparent,  without  further  comment,  that 
it  is  impossible  to  imagine  stronger  evidence  in  favour 
of  natural  selection  as  a  true  cause  in  nature,  than  is 
furnished  by  this  culminating  fact  in  the  matter  of 


FlG   li*. — Three'cases  of  mimicry.    Drawn  from  nature  :  first  two  pairs  nat.  size.. 
last  pair  |  (/?.  Coll.  Surf.  Mus.). 


Evidences  of  Theory  of  Natural  Selection.  329 


protective  resemblance,  whereby  it  is  shown  that  a 
species  of  one  genus,  family,  or  even  order,  will 
accurately  mimic  the  appearance  of  a  species  be- 
longing to  another  genus,  family,  or  order,  so  as  to 
deceive  its  natural  enemies  into  mistaking  it  for  a 
creature  of  so  totally  different  a  kind.  And  it  must 
be  added  that  while  this  fact  of  mimicry  is  of  ex- 


VESPA 


VOL,     BoMBY'LArJs.  BOMBU'S   LapiDARiJs. 

FIG.  114. — Two  further  cases  of  mimicry;  flies  resembling  a  wasp  in 
the  one  and  a  bee  in  the  other.  Drawn  from  nature  :  nat.  size  (J?. 
Coll.  Surg.  Mus.). 

traordinarily  frequent  occurrence,  there  can  be  no 
possibility  of  our  mistaking  its  purpose.  For  the  fact 
is  never  observable  except  in  the  case  of  species  which 
occupy  the  same  area  or  district. 

Such  being  what  appears  to  me  the  only  reasonable 
view  of  the  matter,  I  will  now  conclude  this  chapter 
on  the  evidences  of  natural  selection  as  at  all  events  the 


\*. 


FlG.  1  1  5.  —A  case  of  mimicry  where  a  non- 
venomous  one.     Drawn  from  nature  : 


nomous  species  of  snake  resemble 
nat.  size  (R.  Coll.  Siirg.  Mus.). 


Evidences  of  Theory  of  Natural  Selection.  3  3 1 

main  factor  of  organic  evolution,  by  simply  adding 
illustrations  of  two  further  cases  of  mimicry,  which  are 
perhaps  even  more  remarkable  than  any  of  the  fore- 
going examples.  The  first  of  the  two  (Fig.  1 15)  speaks 
for  itself.  The  second  will  be  rendered  intelligible  by 
the  following  few  words  of  explanation. 

There  are  certain  ants  of  the  Amazons  which 
present  the  curious  instinct  of  cutting  off  leaves  from 
trees,  and  carrying  them  like  banners  over  their 
heads  to  the  hive,  as  represented  in  Fig.  116,  B,  where 
one  ant  is  shown  without  a  leaf,  and  the  others  each 
with  a  leaf.  Their  object  in  thus  collecting  leaves  is 
probably  that  of  growing  a  fungus  upon  the  "soil" 
which  is  furnished  by  the  leaves  when  decomposing. 
But,  be  this  as  it  may l,  the  only  point  we  are  now  con- 
cerned with  is  the  appearance  which  these  ants  present 
when  engaged  in  their  habitual  operation  of  carrying 
leaves.  For  it  has  been  recently  observed  by  Mr.  W. 
L.  Sclater,  that  in  the  localities  where  these  hymenop- 
terous  insects  occur,  there  occurs  also  a  homopterous 
insect  which  mimics  the  ant,  leaf  and  all,  in  a  wonder- 
fully deceptive  manner.  The  leaf  is  imitated  by  the 
thin  flattened  body  of  the  insect,  "  which  in  its  dorsal 
aspect  is  so  compressed  laterally  that  it  is  no  thicker 
than  a  leaf,  and  terminates  in  a  sharp  jagged  edge." 
The  colour  is  exactly  the  same  as  that  of  a  leaf, 
and  the  brown  legs  show  themselves  beneath  the 
green  body  in  just  the  same  way  as  those  of  the  ant 
show  themselves  beneath  the  leaf.  So  that  both  the 
form  and  the  colouring  of  the  homopterous  insect  has 
been  brought  to  resemble,  with  singular  exactness, 

1  For  a  full  account  of  this  instinct  and  its  probable  purpose,  see 
Animal  Intelligence,  pp.  93-6. 


332  Darwin,  and  after  Darwin. 

those  belonging  to  a  different  order  of  insect,  when 
the  latter  is  engaged  in  its  peculiar  avocation.  A 
glance  at  the  figure  is  enough  to  show  the  means 
employed  and  the  result  attained.  In  A,  an  ant  and 
its  mimic  are  represented  as  about  2\  times  their 
natural  size,  and  both  proceeding  in  the  same  direction. 
It  ought  to  be  mentioned,  however,  that  in  reality 
the  margin  of  the  leaf  is  seldom  allowed  to  retain  its 
natural  serrations  as  here  depicted  :  the  ants  usually 
gnaw  the  edge  of  the  real  leaf,  so  that  the  margin  of 
the  false  one  bears  an  even  closer  resemblance  to  it 
than  the  illustration  represents.  B  is  a  drawing  from 
life  of  a  group  of  five  ants  carrying  leaves,  and  their 
mimic  walking  beside  them1. 

1  Both  drawings  are  reproduced  from  Mr.  Poulton's  paper  upon  the 
subject  (Proc,  Zool.  Soc.,  June  16,  1891). 


Hg.116. 
PROTECTIVE  'MTMLCEY. 


CHAPTER   IX. 

CRITICISMS  OF  THE  THEORY  OF  NATURAL 
SELECTION. 

I  WILL  now  proceed  to  consider  the  various  objec- 
tions and  difficulties  which  have  hitherto  been  advanced 
against  the  theory  of  natural  selection. 

Very  early  in  the  day  Owen  hurled  the  weight  of 
his  authority  against  the  new  theory,  and  this  with  a 
strength  of  onslaught  which  was  only  equalled  by  its 
want  of  judgment.  Indeed,  it  is  painfully  apparent 
that  he  failed  to  apprehend  the  fundamental  principles 
of  the  Darwinian  theory.  For  he  says  : — 

Natural  Selection  is  an  explanation  of  the  process  [of  trans- 
mutation] of  the  same  kind  and  value  as  that  which  has  been 
proffered  of  the  mystery  of  "  secretion."  For  example,  a  par- 
ticular mass  of  matter  in  a  living  animal  takes  certain  elements 
out  of  the  blood,  and  rejects  them  as  "  bile."  Attributes  were 
given  to  the  liver  which  can  only  be  predicated  of  the  whole 
animal ;  the  "  appetency  "  of  the  liver,  it  was  said,  was  for  the 
elements  of  bile,  and  "biliosity,"  or  the  "hepatic  sensation," 
guided  the  gland  to  their  secretion.  Such  figurative  language, 
I  need  not  say,  explains  absolutely  nothing  of  the  nature  of 
bilification  *. 

Assuredly,  it  was  needless  for  Owen  to  say  that 
figurative  language  of  this  kind  explains  nothing;  but 

1  Anatomy  of  Vertebrates,  vol.  iii.  p.  794. 


334          Darwin,  and  after  Darwin. 

it  was  little  less  than  puerile  in  him  to  see  no  more 
in  the  theory  of  natural  selection  than  such  a  mere 
figure  of  speech.  To  say  that  the  liver  selects  the 
elements  of  bile,  or  that  nature  selects  specific  types, 
may  both  be  equally  unmeaning  re-statements  of  facts  ; 
but  when  it  is  explained  that  the  term  natural  selec- 
tion, unlike  that  of  "  hepatic  sensation,"  is  used  as 
a  shorthand  expression  for  a  whole  group  of  well- 
known  natural  causes — struggle,  variation,  survival, 
heredity, — then  it  becomes  evidence  of  an  almost 
childish  want  of  thought  to  affirm  that  the  expression 
is  figurative  and  nothing  more.  The  doctrine  of 
natural  selection  may  be  a  huge  mistake  ;  but,  if  so, 
this  is  not  because  it  consists  of  any  unmeaning 
metaphor :  it  can  only  be  because  the  combination  of 
natural  causes  which  it  suggests  is  not  of  the  same 
adequacy  in  fact  as  it  is  taken  to  be  in  theory. 

Owen  further  objected  that  the  struggle  for  existence 
could  only  act  as  a  cause  of  the  extinction  of  species, 
not  of  their  origination— a  view  of  the  case  which  again 
shows  on  his  part  a  complete  failure  to  grasp  the 
conception  of  Darwinism.  Acting  alone,  the  struggle 
for  existence  could  only  cause  extermination ;  but 
acting  together  with  variation,  survival,  and  heredity, 
it  may  very  well — for  anything  that  Owen,  or  others 
who  followed  in  this  line  of  criticism,  show  to  the 
contrary — have  produced  every  species  of  plant  and 
animal  that  has  ever  appeared  upon  the  face  of  the 
earth. 

Another  and  closely  allied  objection  is,  that  the 
theory  of  natural  selection  "  personifies  an  abstrac- 
tion." Or,  as  the  Duke  of  Argyll  states  it,  the  theory 
is  "  essentially  the  image  of  mechanical  necessity 


Criticisms  of  Theory  of  Natural  Selection.  335 

concealed  under  the  clothes,  and  parading  in  the  mask, 
of  mental  purpose.  The  word  '  natural '  suggests 
Matter, and  the  physical  forces.  The  word  '  selection' 
suggests  Mind,  and  the  powers  of  choice."  This,  how- 
ever, is  a  mere  quarrelling  about  words.  Darwin 
called  the  principle  which  he  had  discovered  by  the 
name  natural  selection  in  order  to  mark  the  analogy 
between  it  and  artificial  selection.  No  doubt  in  this 
analogy  there  is  not  necessarily  supposed  to  be  in 
nature  any  counterpart  to  the  mind  of  the  breeder,  nor, 
therefore,  to  his  powers  of  intelligent  choice.  But 
there  is  no  need  to  limit  the  term  selection  (se  and  lego, 
Gr.  Ae'yco)  to  powers  of  intelligent  choice.  As  previously 
remarked,  a  bank  of  sea- weed  on  the  sea-shore  may  be 
said  to  have  been  selected  by  the  waves  from  all  the 
surrounding  sand  and  stones.  Similarly,  we  may  say 
that  grain  is  selected  from  chaff  by  the  wind  in  the 
process  of  winnowing  corn.  Or,  if  it  be  thought  that 
there  is  any  ambiguity  involved  in  such  a  use  of  the 
term  in  the  case  of  '•  Natural  Selection/'  there  is  no 
objection  to  employing  the  phrase  which  has  been 
coined  by  Mr.  Spencer  as  its  equivalent — namely, 
"  Survival  of  the  Fittest."  The  point  of  the  theory  is, 
that  those  organisms  which  are  best  suited  to  their 
surroundings  are  allowed  to  live  and  to  propagate, 
while  those  which  are  less  suited  are  eliminated  ;  and 
whether  we  call  this  process  a  process  of  selection,  or 
call  it  by  any  other  name,  is  clearly  immaterial. 

A  material  question  is  raised  only  when  it  is  asked 
whether  the  process  is  one  that  can  be  ascribed  to 
causation  strictly  natural.  It  is  often  denied  that 
such  is  the  case,  on  the  ground  that  natural  selection 
does  not  originate  the  variations  which  it  favours, 


336          Darwin,  and  after  Darwin. 

but  depends  upon  the  variations  being  supplied  by 
some  other  means.  For,  it  is  said,  all  that  natural 
selection  does  is  to  preserve  the  suitable  variations 
after  they  have  arisen.  Natural  selection  does  not 
cause  these  suitable  variations ;  and  therefore,  it  is 
argued,  Darwin  and  his  followers  are  profoundly 
mistaken  in  representing  the  principle  as  one  which 
produces  adaptations.  Now,  although  this  objection 
has  been  put  forward  by  some  of  the  most  intelligent 
minds  in  our  generation,  it  appears  to  me  to  betoken 
some  extraordinary  failure  to  appreciate  the  very 
essence  of  Darwinian  doctrine.  No  doubt  it  is  per- 
fectly true  that  natural  selection  does  not  produce 
variations  of  any  kind,  whether  beneficial  or  other- 
wise. But  if  it  be  granted  that  variations  of  many 
kinds  are  occurring  in  every  generation,  and  that 
natural  selection  is  competent  to  preserve  the  more 
favourable  among  them,  then  it  appears  to  me 
unquestionable  that  this  principle  of  selection  deserves 
to  be  regarded  as,  in  the  full  sense  of  the  word,  a 
natural  cause.  The  variations  being  expressly  re- 
garded by  the  theory  as  more  or  less  promiscuous1, 

1  The  degree  in  which  variability  is  indefinite,  or,  on  the  contrary, 
determinate,  is  a  question  which  is  not  jet  ripe  for  decision — nor  even, 
in  my  opinion,  for  dicussion.  But  I  may  here  state  the  following  general 
principles  with  regard  to  it 

(1)  It  is  evident  that  up  to  some  point  or  another  variations  must  be 
pre-determined  in  definite  lines.    Men  do  not  gather  grapes  from  thorns, 
figs  from  thistles,  nor  even  moss-roses  from  sweet-briars.    In  other  words, 
"  the  nature  of  the  organism  "  in  all  cases  necessitates  the  limiting  of 
variations  within  certain  bounds. 

(2)  But  when  the  question  is  as  to  what  these  bounds  may  be,  we  can 
only  answer  in  a  general  way  that,  according  to  the  general  theory  of 
evolution,  they  must  be  such  as  are  imposed  by  heredity,  coupled  with 
the  degree  to  which  external  conditions  of  life  (and  possibly  also  use- 
inheritance)    are   capable,   in    given    cases,    of   modifying    congenital 


Criticisms  of  Theory  of  Natural  Selection.  337 

survival  of  the  fittest  becomes  the  winnowing  fan, 
whose  function  it  is  to  eliminate  all  the  less  fit  in 
each  generation,  in  order  to  preserve  the  good  grain, 
out  of  which  to  constitute  the  next  generation.  And 
as  this  process  is  supposed  to  be  continuous  through 
successive  generations,  its  action  is  supposed  to  be 
cumulative,  till  from  the  eye  of  a  worm  there  is 
gradually  developed  the  eye  of  an  eagle.  Therefore 
it  follows  from  these  suppositions  (which  are  not 
disputed  by  the  present  objection),  that  if  it  had  not 
been  for  the  process  of  selection,  such  development 
would  never  have  been  begun  ;  and  that  in  the  exact 
measure  of  its  efficiency  will  the  development  pro- 
ceed. But  any  agency  without  the  operation  of 
which  a  result  cannot  take  place  may  properly  be 
designated  the  cause  of  that  result :  it  is  the  agency 
which,  in  co-operation  with  all  the  other  agencies 
in  the  cosmos,  produces  that  result. 

characters.  These  are  the  only  causes  which  the  theory  of  descent  can 
consistently  recognise  as  producing  variations  in  determinate  directions. 

(3)  Inasmuch  as  variation  presupposes  the  existence  of  parts  that 
vary,  and  inasmuch  as  the  variation  of  parts  can  only  be  in  the  alterna- 
tive directions  of  increase  or  decrease  around  an  average,  it  follows  that, 
in  the  first  instance  at  all  events,  every  variation,  if  determinate,  must 
be  so  only  in  one  or  other  of  these  two  opposite  directions. 

(4)  In  as  far  as  variations  are  summated  in  successive  generations,  so 
as  eventually  to  give  rise  to  new  structures,  organs,  mechanisms,  &c,, 
natural  selection  is  theoretically  competent  to  explain  the  facts,  without 
our  having  to  postulate  the  operation  of  unknown  causes  producing 
variations  in  determinate  lines, — or  not  fuither  than  is  stated  in  para- 
graphs i  and  2. 

(5)  Nevertheless,  it  does  not  follow  that  there  are  not  such  other 
unknown  causes ;  and,  if  there  are,  of  course  the  importance  of  natural 
selection  as  a  cause  of  adaptive  modification  would  be  limited  in  pro- 
portion to  their  number  and  the  extent  of  their  operation.    But  it  is  for 
those  who,  like  the  late  Professors  Asa  Gray  and  Nageli,  maintain  the 
existence  of  such  causes,  to  substantiate  their  belief  by  indicating  them. 


338          Darwin,  and  after  Darwin. 

Take  any  analogous  case.  The  selective  agency 
of  specific  gravity  which  is  utilised  in  gold-washing 
does  not  create  the  original  differences  between  gold- 
dust  and  dust  of  all  other  kinds.  But  these  differ- 
ences being  presented  by  as  many  different  bodies 
in  nature,  the  gold -washer  takes  advantage  oi  the 
selective  agency  in  question,  and,  by  using  it  as  a 
cause  of  segregation,  is  enabled  to  separate  the  gold 
from  all  the  earths  with  which  it  may  happen  to  be 
mixed.  So  far  as  the  objects  of  the  gold-washer  are 
concerned,  it  is  immaterial  with  what  other  earths 
the  gold-dust  may  happen  to  be  mixed.  For 
although  gold-dust  may  occur  in  intimate  association 
with  earths  of  various  kinds  in  various  proportions, 
and  although  in  each  case  the  particular  admixture 
which  occurs  must  have  been  due  to  definite  causes, 
these  things,  in  relation  to  the  selective  process  of 
the  washer,  are  what  is  called  accidental :  that  is 
to  say,  they  have  nothing  to  do  with  the  causative 
action  of  the  selective  process.  Now,  in  precisely 
the  same  sense  Darwin  calls  the  multitudinous  varia- 
tions of  plants  and  animals  accidental.  By  so  calling 
them  he  expressly  says  he  does  not  suppose  them 
to  be  accidental  in  the  sense  of  not  all  being  due 
to  definite  causes.  But  they  are  accidental  in  rela- 
tion to  the  sifting  process  of  natural  selection :  all 
that  they  have  to  do  is  to  furnish  the  promiscuous 
material  on  which  this  sifting  process  acts. 

Or  let  us  take  an  even  closer  analogy.  The  power 
of  selective  breeding  by  man  is  so  wonderful,  that  in 
the  course  of  successive  generations  all  kinds  of 
peculiarities  as  to  size,  sjiape,  colour,  special  appen- 
dages or  abortions,  &c.,  can  be  produced  at  pleasure, 


Criticisms  of  Theory  of  Natural  Selection.  339 

as  we  saw  in  the  last  chapter.  Now  all  the  promis- 
cuous variations  which  are  supplied  to  the  breeder, 
and  out  of  which,  by  selecting  only  those  that  are 
suited  to  his  purpose,  he  is  able  to  produce  the 
required  result— all  those  promiscuous  variations,  in 
relation  to  that  purpose,  are  accidental.  Therefore 
the  selective  agency  of  the  breeder  deserves  to  be 
regarded  as  the  cause  of  that  which  it  produces,  or 
of  that  which  could  not  have  been  produced  but  for 
the  operation  of  such  agency.  But  where  is  thf 
difference  between  artificial  and  natural  selection  in 
this  respect?  And,  if  there  is  no  difference,  is  not 
natural  selection  as  much  entitled  to  be  regarded  as  a 
true  cause  of  the  origin  of  natural  species,  as  artificial 
selection  is  to  be  regarded  as  a  true  cause  of  our 
domesticated  races  ?  Here,  as  in  the  case  of  the 
previous  illustration,  if  there  be  any  ambiguity  in 
speaking  of  variations  as  accidental,  it  arises  from 
the  incorrect  or  undefined  manner  in  which  the  term 
"  accidental "  is  used  by  Darwin's  critics.  In  its 
original  and  philosophically-correct  usage,  the  term 
"accident"  signifies  a  property  or  quality  not  essential 
to  our  conception  of  a  substance :  hence,  it  has  come 
to  mean  anything  that  happens  as  a  result  of  unfore- 
seen causes — or,  lastly,  that  which  is  causeless.  But, 
as  we  know  that  nothing  can  happen  without  causes 
of  some  kind,  the  term  "  accident "  is  divested  of  real 
meaning  when  it  is  used  in  the  last  of  these  senses. 
Yet  this  is  the  sense  that  is  sought  to  be  placed  upon 
it  by  the  objection  which  we  are  considering.  If  the 
objectors  will  but  understand  the  term  in  its  correct 
philosophical  sense — or  in  the  only  sense  in  which 
it  presents  any  meaning  at  all,— they  will  see  that 
Z  2 


34-O          Darwin,  and  after  Darwin. 

Darwinians  are  both  logically  and  historically  justified 
in  employing  the  word  "  accidental "  as  the  word 
which  serves  most  properly  to  convey  the  meaning 
that  they  intend — namely,  variations  due  to  causes 
accidental  to  the  struggle  for  existence.  Similarly, 
when  it  is  said  that  variations  are  "  spontaneous," 
or  even  "fortuitous,"  nothing  further  is  meant  than 
that  we  do  not  know  the  causes  which  lead  to  them,  and 
that,  so  far  as  the  principle  of  selection  is  concerned, 
it  is  immaterial  what  these  causes  may  be.  Or,  to 
revert  to  our  former  illustration,  the  various  weights 
of  different  kinds  of  earths  are  no  doubt  all  due  to 
definite  causes ;  but,  in  relation  to  the  selective 
action  of  the  gold-washer,  all  the  different  weights 
of  whatever  kinds  of  earth  he  may  happen  to  in- 
clude in  his  washing-apparatus  are,  strictly  speaking, 
accidental.  And  as  at  different  washings  he  meets 
with  different  proportions  of  heavy  earths  with  light 
ones,  and  as  these  "variations "are  immaterial  to  him, 
he  may  colloquially  speak  of  them  as  "  fortuitous,"  or 
due  to  "  chance,"  even  though  he  knows  that  at  each 
washing  they  must  have  been  determined  by  definite 
causes. 

More  adequately  to  deal  with  this  merely  formal 
objection,  however,  would  involve  more  logic-chop- 
ping than  is  desirable  on  the  present  occasion.  But 
I  have  already  dealt  with  it  fully  elsewhere, — viz.  in 
The  Contemporary  Review  for  June,  1888,  to  which 
therefore  I  may  refer  any  one  who  is  interested  in 
dialectics  of  this  kind  l. 

1  Within  the  last  few  months  this  objection  has  been  presented  anew 
by  Mr.  D.  Syme,  whose  book  On  the  Modification  of  Organisms  exhibils 
a  curious  combination  of  shrewd  criticisms  with  almost  ludicrous  mis- 


Criticisms  of  Theory  of  Natural  Selection.  341 

I  will  now  pass  on  to  consider  another  miscon- 
ception of  the  Darwinian  theory,  which  is  very 
prevalent  in  the  public  mind.  It  is  virtually  asked, 
If  some  species  are  supposed  to  have  been  improved 
by  natural  selection,  why  have  not  all  species  been 
similarly  improved?  Why  should  not  all  inverte- 


understandings.  One  of  the  latter  it  is  necessary  to  state,  because  it 
pervades  the  quotation  which  I  am  about  to  supply.  He  everywhere 
compares  "natural  selection"  with  "the  straggle  for  existence,"  uses 
them  as  convertible  terms,  and  while  absurdly  stating  that  "  Darwin 
defines  natural  selection  as  the  struggle  for  existence,"  complains  of 
"  the  liability  of  error,  both  on  his  own  part  and  on  the  part  of  his 
readers,"  which  arises  from  his  not  having  everywhere  adhered  to  this 
definition !  (p.  8). 

"  Darwin  has  put  forth  two  distinct  and  contradictory  theories  of  the 
functions  of  natural  selection.  According  to  the  one  theory  natural 
selection  is  selective  or  preservative,  and  nothing  more.  According  to 
the  other  theory  natural  selection  creates  the  variations  (!)...  It  cer- 
tainly seems  absurd  to  speak  of  natural  selection,  or  the  struggle  for 
existence,  as  selective  or  preservative,  for  the  struggle  for  existence 
does  not  preserve  at  all,  not  even  the  fit  variations,  as  both  the  fit 
and  the  unfit  struggle  for  existence,  the  unfit  naturally  more  than  the 
fit,  and  the  fit  are  preserved,  not  in  consequence  of  the  struggle,  but  in 
consequence  of  their  fitness.  Suppose  two  varieties  of  the  same  species 
are  driven,  by  an  increase  of  their  numbers,  to  seek  for  subsistence  in  a 
colder  region  than  they  have  been  accustomed  to,  and  that  one  of  these 
varieties  had  a  hardier  constitution  than  the  other ;  and  let  us  suppose 
that  the  former  withstood  the  severe  climate  better  than  the  latter,  and 
consequently  survived,  while  the  other  perished.  In  this  case  the  hardier 
survived,  not  because  of  the  struggle,  but  because  it  had  a  constitution 
better  adapted  to  the  climate.  I  wish  to  ascertain  if  a  certain  metal  in 
my  possession  is  gold  or  some  baser  metal,  and  I  apply  the  usual  test ; 
but  the  mere  fact  of  my  testing  this  metal  would  not  make  it  gold  or  any 
other  kind  of  metal." 

I  have  thought  it  worth  while  to  quote  this  passage  for  the  sake  of 
showing  the  extraord.nary  confusion  of  mind  which  still  prevails  on  the 
•part  of  Darsvin's  critics,  even  with  reference  to  the  very  fundamental 
parts  of  his  theory.  For,  as  I  have  said,  the  writer  of  this  passage  shows 
himself  a  shrewd  critic  in  some  other  parts  of  his  essay,  where  he  is  not 
engaged  especially  on  the  theory  oi  natural  selection. 


34 2          Darwin,  and  after  Darwin. 

brated  animals  have  risen  into  vertebrated  ?     Or  why 
should  not  all  monkeys  have  become  men  ? 

The  answers  are  manifold.  In  the  first  place,  it 
by  no  means  follows  that  because  an  advance  in 
organization  has  proved  itself  of  benefit  in  the  case 
of  one  form  of  life,  therefore  any  or  every  other 
form  would  have  been  similarly  benefited  by  a 
similar  advance.  The  business  of  natural  selection 
is  to  bring  this  and  that  form  of  life  into  the  closest 
harmony  with  its  environment  that  all  the  conditions 
of  the  case  permit.  Sometimes  it  will  happen  that 
the  harmony  will  admit  of  being  improved  by  an 
improvement  of  organization.  But  just  as  often  it 
will  happen  that  it  will  be  best  secured  by  leaving 
matters  as  they  are.  If,  therefore,  an  organism  has 
already  been  brought  into  a  tolerably  full  degree  of 
harmony  with  its  environment,  natural  selection  will 
not  try  to  change  it  so  long  as  the  environment 
remains  unchanged  ;  and  this,  no  doubt,  is  the  reason 
why  some  species  have  survived  through  enormous 
periods  of  geological  time  without  having  undergone 
any  change.  Again,  as  we  saw  in  a  previous  chapter, 
there  are  yet  other  cases  where,  on  account  of  some 
change  in  the  environment  or  even  in  the  habits  of  the 
organisms  themselves,  adaption  will  be  best  secured 
by  an  active  reversal  of  natural  selection,  with  the 
result  of  causing  degeneration. 

But,  it  is  sometimes  further  urged,  there  are  cases 
where  we  cannot  doubt  that  improvement  of  organi- 
zation would  have  been  of  benefit  to  species;  and 
yet  such  improvement  has  not  taken  place — as,  for  in- 
stance, in  the  case  all  monkeys  not  turning  into  men. 
Here,  however,  we  must  remember  that  the  operation 


Criticisms  of  Theory  of  Natural  Selection.  343 

of  natural  selection  in  any  case  depends  upon  a  variety 
of  highly  complex  conditions;  and,  therefore,  that  the 
fact  of  all  those  conditions  having  been  satisfied  in 
one  instance  is  no  reason  for  concluding  that  they 
must  also  have  been  satisfied  in  other  instances.  Take, 
for  example,  the  case  of  monkeys  passing  into  men. 
The  wonder  to  me  appears  to  be  that  this  improve- 
ment should  have  taken  place  in  even  one  line  of 
descent ;  not  that,  having  taken  place  in  one  line, 
it  should  not  also  have  taken  place  in  other  lines. 
For  how  enormously  complex  must  have  been  the 
conditions — physical,  anatomical,  physiological,  psy- 
chological, sociological — which  by  their  happy  con- 
junction first  began  to  raise  the  inarticulate  cries  of 
an  ape  into  the  rational  speech  of  a  man.  Therefore, 
the  more  that  we  appreciate  the  superiority  of  a  man 
to  an  ape,  the  less  ought  we  to  countenance  this 
supposed  objection  to  Darwin's  theory — namely,  that 
natural  selection  has  not  effected  the  change  in  more 
than  one  line  of  descent. 

Even  in  the  case  of  two  races  of  mankind  where 
one  has  risen  higher  in  the  scale  of  civilization 
than  another,  it  is  now  generally  impossible  to  assign 
the  particular  causes  of  the  difference ;  much  more, 
then,  must  this  be  impossible  in  the  case  of  still  more 
remote  conditions  which  have  led  to  the  divergence 
of  species.  The  requisite  variations  may  not  have 
arisen  in  the  one  line  of  descent  which  did  arise  in 
the  other ;  or  if  they  did  arise  in  both,  some 
counterbalancing  disadvantages  may  have  attended 
their  initial  development  in  the  one  case  which 
did  not  obtain  in  the  other.  In  short,  where 
so  exceedingly  complex  a  play  of  conditions  are 


344          Darwin,  and  after  Darwin. 

concerned,  the  only  wonder  would  be  if  two  different 
lines  of  descent  had  happened  to  present  two  in- 
dependent and  yet  perfectly  parallel  lines  of  history. 

These  general  considerations  would  apply  equally 
to  the  great  majority  of  other  cases  where  some  types 
have  made  great  advances  upon  others,  notwithstand- 
ing that  we  can  see  no  reason  why  the  latter  should 
not  in  this  respect  have  imitated  the  former.  But 
there  is  yet  a  further  consideration  which  must  be 
taken  into  account.  The  struggle  for  existence  is 
always  most  keen  between  closely  allied  species,  be- 
cause, from  the  similarity  of  their  forms,  habits,  needs, 
&c.,  they  are  in  closest  competition.  Therefore  it  often 
happens  that  the  mere  fact  of  one  species  having  made 
an  advance  upon  others  of  itself  precludes  the  others 
from  making  any  similar  advance:  the  field,  so  to 
speak,  has  already  been  occupied  as  regards  that 
particular  improvement,  and  where  the  struggle  for 
existence  is  concerned  possession  is  emphatically  nine 
points  of  the  law.  For  example,  to  return  to  the 
case  of  apes  becoming  men,  the  fact  of  one  rational 
species  having  been  already  evolved  (even  if  the 
rational  faculty  were  at  first  but  dimly  nascent)  must 
make  an  enormous  change  in  the  conditions  as 
regards  the  possibility  of  any  other  such  species  being 
subsequently  evolved — unless,  of  course,  it  be  by 
way  of  descent  from  the  rational  one.  Or,  as  Sir 
Charles  Lyell  has  well  put  it,  two  rational  species  can 
never  coexist  on  the  globe,  although  the  descendants 
of  one  rational  species  may  in  time  become  trans- 
formed into  another  single  rational  species  \ 

In  view  of  such  considerations,  another  and  exactly 
1  Principles  of  Geology,  vol.  ii.  p.  487  (nth  ed.). 


Criticisms  of  Theory  of  Natitral  Selection.  345 

opposite  objection  has  sometimes  been  urged — viz. 
that  we  ought  never  to  find  inferior  forms  of  or- 
ganization in  company  with  superior,  because  in  the 
struggle  for  existence  the  latter  ought  to  have  exter- 
minated the  former.  Or,  to  quote  the  most  recent 
expression  of  this  view,  "in  every  locality  there 
would  only  be  one  species,  and  that  the  most  highly 
organized ;  and  thus  a  few  superior  races  would  par- 
tition the  earth  amongst  them  to  the  entire  exclusion 
of  the  innumerable  varieties,  species,  genera,  and  orders 
which  now  inhabit  it  V  Of  course  to  this  statement 
it  would  be  sufficient  to  enquire,  On  what  would  these 
few  supremely  organized  species  subsist?  Unless 
manna  fell  from  heaven  for  their  especial  benefit,  it 
would  appear  that  such  forms  could  under  no  circum- 
stances be  the  most  improved  forms ;  in  exterminating 
others  on  such  a  scale  as  this,  they  would  themselves 
be  quickly,  and  very  literally,  improved  off  the  face 
of  the  earth.  But  even  when  the  statement  is  not 
made  in  so  extravagant  a  form  as  this,  it  must  neces- 
sarily be  futile  as  an  objection  unless  it  has  first  been 
shown  that  we  know  exactly  all  the  conditions  of  the 
complex  struggle  for  existence  between  the  higher 
and  lower  forms  in  question.  And  this  it  is  impos- 
sible that  we  ever  can  know.  The  mere  fact  that 
one  form  has  been  changed  in  virtue  of  this  struggle 
must  in  many  cases  of  itself  determine  a  change  in 
the  conditions  of  the  struggle.  Again,  the  other 
and  closely  allied  forms  (and  these  furnish  the  best 
grounds  for  the  objection)  may  also  have  under- 
gone defensive  changes,  although  these  may  be 
less  conspicuous  to  our  observation,  or  perhaps  less 
1  Syme,  on  the  Modification  of  Organisms,  p.  46. 


346          Darwin,  and  after  Darwin. 

suggestive  of  "improvement"  to  our  imperfect 
means  of  judging.  Lastly,  not  to  continue  citing 
an  endless  number  of  such  considerations,  there  is 
the  broad  fact  that  it  is  only  to  those  cases  where, 
for  some  reason  or  another,  the  lower  forms  have 
not  been  exposed  to  a  struggle  of  fatal  intensity,  that 
the  objection  applies.  But  we  know  that  in  millions 
of  other  cases  the  lower  (i.e.  less  fitted)  forms  have 
succumbed,  and  therefore  I  do  not  see  that  the  ob- 
jection has  any  ground  to  stand  upon.  That  there  is 
a  general  tendency  for  lower  forms  to  yield  their 
places  to  higher  is  shown  by  the  gradual  advance  of 
organization  throughout  geological  time  ;  for  if  all  the 
inferior  forms  had  survived,  the  earth  could  not  have 
contained  them,  unless  she  had  been  continually 
growing  into  something  like  the  size  of  Jupiter. 
And  if  it  be  asked  why  any  of  the  inferior  forms 
have  survived,  the  answer  has  already  been  given, 
as  above. 

There  is  only  one  other  remark  to  be  made  in  this 
connexion.  Mr.  Syme  chooses  two  cases  as  illus- 
trations of  the  supposed  difficulty.  These  are  suf- 
ficiently diverse — viz.  Foraminifera  and  Man.  Touch- 
ing the  former,  there  is  nothing  that  need  be  added 
to  the  general  answer  just  given.  But  with  regard  to 
the  latter  it  must  be  observed  that  the  dominion  of 
natural  selection  as  between  different  races  of  man- 
kind is  greatly  restricted  by  the  presence  of  rationality. 
Competition  in  the  human  species  is  more  concerned 
with  wits  and  ideas  than  with  nails  and  teeth  ;  and 
therefore  the  "struggle"  between  man  and  man  is 
not  so  much  for  actual  being,  as  for  well-being.  Con- 
sequently, in  regard  to  the  present  objection,  the 


Criticisms  of  Theory  of  Natural  Selection.  347 

human  species  furnishes  the  worst  example  that  could 
have  been  chosen. 

Hitherto  I  have  been  considering  objections  which 
arise  from  misapprehensions  of  Darwin's  theory.  I 
will  now  go  on  to  consider  a  logically  sound  ob- 
jection, which  nevertheless  is  equally  futile,  because, 
although  it  does  not  depend  on  any  misapprehension 
of  the  theory,  it  is  not  itself  supported  by  fact 

The  objection  is  the  same  as  that  which  we  have 
already  considered  in  relation  to  the  general  theory  of 
descent — namely,  that  similar  organs  or  structures 
are  to  be  met  with  in  widely  different  branches  of  the 
tree  of  life.  Now  this  would  be  an  objection  fatal  to 
the  theory  of  natural  selection,  supposing  these  organs 
or  structures  in  the  cases  compared  are  not  merely 
analogous,  but  also  homologous.  For  it  would  be 
incredible  that  in  two  totally  different  lines  of  descent 
one  and  the  same  structure  should  have  been  built  up 
independently  by  two  parallel  series  of  variations,  and 
that  in  these  two  lines  of  descent  it  should  always  and 
independently  have  ministered  to  the  same  function. 
On  the  other  hand,  there  would  be  nothing  against 
the  theory  of  natural  selection  in  the  fact  that  two 
structures,  not  homologous,  should  come  by  inde- 
pendent variation  in  two  different  lines  of  descent  to 
be  adapted  to  perform  the  same  function.  For  it 
belongs  to  the  very  essence  of  the  theory  of  natural 
selection  that  a  useful  function  should  be  secured  by 
favourable  variations  of  whatever  structural  material 
may  happen  to  be  presented  by  different  organic 
types.  Flying,  for  instance,  is  a  very  useful  function, 
and  it  has  been  developed  independently  in  at  least 


348          Darwin,  and  after  Darwin. 

four  different  lines  of  descent — namely,  the  insects, 
reptiles,  birds,  and  mammals.  Now  if  in  all,  or  in- 
deed in  any,  of  these  four  cases  the  wings  had  been 
developed  on  the  same  anatomical  pattern,  so  as  not 
only  to  present  the  analogical  resemblance  which  it  is 
necessary  that  they  should  present  in  order  to  dis- 
charge their  common  function  of  flying,  but  likewise 
an  homologous  or  structural  resemblance,  showing 
that  they  had  been  formed  on  the  same  anatomical 
"  plan," — if  such  has  been  the  case,  I  say,  the  theory 
of  natural  selection  would  certainly  be  destroyed. 

Now  it  has  been  alleged  by  competent  naturalists 
that  there  are  several  such  cases  in  organic  nature. 
We  have  already  noticed  in  a  previous  chapter 
(pp.  58,  59),  that  Mr.  Mivart  has  instanced  the  eye 
of  the  cuttle-fish  as  not  only  analogous  to,  but  also 
homologous  with,  the  eye  of  a  true  fish — that  is  to 
say,  the  eye  of  a  mollusk  with  the  eye  of  a  vertebrate. 
And  he  has  also  instanced  the  remarkable  resemblance 
of  a  shrew  to  a  mouse — that  is,  of  an  insectivorous 
mammal  to  a  rodent — not  to  mention  other  cases. 
In  the  chapter  alluded  to  these  instances  of  homo- 
logy,  alleged  to  occur  in  different  branches  of  the  tree 
of  life,  were  considered  with  reference  to  the  process 
of  organic  evolution  as  a  fact :  they  are  now  being 
considered  with  reference  to  the  agency  of  natural 
selection  as  a  method.  And  just  as  in  the  former 
case  it  was  shown,  that  if  any  such  alleged  instances 
could  be  proved,  the  proof  would  be  fatal  to  the 
general  theory  of  organic  evolution  by  physical 
causes,  so  in  the  present  case,  if  this  could  be 
proved,  it  would  be  equally  fatal  to  the  more  spe- 
cial theory  of  natural  selection.  But,  as  we  have 


Criticisms  of  Theory  of  Natural  Selection.  349 

before  seen,  no  single  case  of  this  kind  has  ever  been 
made  out ;  and,  therefore,  not  only  does  this  sup- 
posed objection  fall  to  the  ground,  but  in  so  doing  it 
furnishes  an  additional  argument  in  favour  of  natural 
selection.  For  in  the  earlier  chapter  just  alluded  to 
I  showed  that  this  great  and  general  fact  of  our  no- 
where being  able  to  find  two  homologous  structures 
in  different  branches  of  the  tree  of  life,  was  the 
strongest  possible  testimony  in  favour  of  the  theory 
of  evolution.  And,  by  parity  of  reasoning,  I  now 
adduce  it  as  equally  strong  evidence  of  natural  selec- 
tion having  been  the  cause  of  adaptive  structures, 
independently  developed  in  all  the  different  lines  of 
descent.  For  the  alternative  is  between  adaptations 
having  been  caused  by  natural  selection  or  by  super- 
natural design.  Now,  if  adaptations  were  caused  by 
natural  selection,  we  can  very  well  understand  why 
they  should  never  be  homologous  in  different  lines  of 
descent,  even  in  cases  where  they  have  been  brought 
to  be  so  closely  analogous  as  to  have  deceived  so 
good  a  naturalist  as  Mr.  Mivart.  Indeed,  as  I  have 
already  observed,  so  well  can  we  understand  this, 
that  any  single  instance  to  the  contrary  would  be 
sufficient  to  destroy  the  theory  of  natural  selection  in 
toto,  unless  the  structure  be  one  of  a  very  simple  type. 
But  on  the  other  hand,  it  is  impossible  to  suggest 
any  rational  explanation  why,  if  all  adaptations  are 
due  to  supernatural  design,  such  scrupulous  care 
should  have  been  taken  never  to  allow  homologous 
adaptations  to  occur  in  different  divisions  of  the  animal 
or  vegetable  kingdoms.  Why,  for  instance,  should 
the  eye  of  a  cuttle-fish  not  have  been  constructed  on 
the  same  ideal  pattern  as  that  of  vertebrate  ?  Or  why, 


350          Darwin,  and  after  Darwin. 

among  the  thousands  of  vertebrated  species,  should  no 
one  of  their  eyes  be  constructed  on  the  ideal  pattern 
that  was  devised  for  the  cuttle-fish  ?  Of  course  it  may 
be  answered  that  perhaps  there  was  some  hidden  reason 
why  the  design  should  never  have  allowed  an  adapta- 
tion which  it  had  devised  for  one  division  of  organic 
nature  to  appear  in  another — even  in  cases  where  the 
new  design  necessitated  the  closest  possible  resem- 
blance in  everything  else,  save  in  the  matter  of  anatomi- 
cal homology.  Undoubtedly  such  may  have  been  the 
case — or  rather  such  must  have  been  the  case — if  the 
theory  of  special  design  is  true.  But  where  the  ques- 
tion is  as  to  the  truth  of  this  theory,  I  think  there  can 
be  no  doubt  that  its  rival  gains  an  enormous  advan- 
tage by  being  able  to  explain  why  the  facts  are  such 
as  they  are,  instead  of  being  obliged  to  take  refuge 
in  hypothetical  possibilities  of  a  confessedly  unsub- 
stantiated and  apparently  unsubstantial  kind. 

Therefore,  as  far  as  this  objection  to  the  theory  of 
natural  selection  is  concerned — or  the  allegation  that 
homologous  structures  occur  in  different  divisions  of 
organic  nature — not  only  does  it  fall  to  the  ground, 
but  positively  becomes  itself  converted  into  one  of  the 
strongest  arguments  in  favour  of  the  theory.  As 
soon  as  the  allegation  is  found  to  be  baseless,  the 
very  fact  that  it  cannot  be  brought  to  bear  upon  any 
one  of  all  the  millions  of  adaptive  structures  in 
organic  nature  becomes  a  fact  of  vast  significance  on 
the  opposite  side. 

The  next  difficulty  to  which  I  shall  allude  is  that 
of  explaining  by  the  theory  of  natural  selection  the 
preservation  of  the  first  beginnings  of  structures  which 


Criticisms  of  Theory  oj  A  atural  Selection.  3  5 1 

are  then  useless,  though  afterwards,,  when  more  fully 
developed,  they  become  useful.  For  it  belongs  to 
the  very  essence  of  the  theory  of  natural  selection, 
that  a  structure  must  be  supposed  already  useful 
before  it  can  come  under  the  influence  of  natural 
selection :  therefore  the  theory  seems  incapable  of 
explaining  the  origin  and  conservation  of  incipient 
organs,  or  organs  which  are  not  yet  sufficiently 
developed  to  be  of  any  service  to  the  organisms 
presenting  them. 

This  objection  is  one  that  has  been  advanced  by 
all  the  critics  of  Darwinism  ;  but  has  been  presented 
with  most  ability  and  force  by  the  Duke  of  Argyll.  I 
will  therefore  state  it  in  his  words. 

If  the  doctrine  of  evolution  be  true— that  is  to  say,  if  all 
organic  creatures  have  been  developed  by  ordinary  generation 
from  parents— then  it  follows  of  necessity  that  the  primaeval 
germs  must  have  contained  potentially  the  whole  succeeding 
series.  Moreover,  if  that  series  has  been  developed  gradually 
and  very  slowly,  it  follows,  also  as  a  matter  of  necessity,  that 
every  modification  of  structure  must  have  been  functionless  at 
first,  when  it  began  to  appear. .  .  .  Things  cannot  be  selected 
until  they  have  first  been  produced.  Nor  can  any  structure 
be  selected  by  utility  in  the  struggle  for  existence  until  it  has 
not  only  been  produced,  but  has  been  so  far  perfected  as  to 
actually  be  used. 

The  Duke  proceeds  to  argue  that  all  adaptive 
structures  must  therefore  originally  have  been  due 
to  special  design  :  in  the  earlier  stages  of  their  develop- 
ment they  must  all  have  been  what  he  calls  "pro- 
phetic germs."  Not  yet  themselves  of  any  use, 
and  therefore  not  yet  capable  of  being  improved  by 
natural  selection,  both  in  their  origin  and  in  the  first 
stages  (at  all  events)  of  their  development,  they  must 


352          Darwin,  and  after  Darwin. 

be  regarded  as  intentionally  preparatory  to  the 
various  uses  which  they  subsequently  acquire. 

Now  this  argument,  forcible  as  it  appears  at  first 
sight,  is  really  at  fault  both  in  its  premiss  and  in  its 
conclusion.  By  which  I  mean  that,  in  the  first  place 
the  premiss  is  not  true,  and,  in  the  next  place,  that 
even  if  it  were,  the  conclusion  would  not  necessarily 
follow.  The  premiss  is,  "that  every  modification  of 
structure  must  have  been  functionless  at  first,  when  it 
began  to  appear ; "  and  the  conclusion  is,  that,  qua 
functionless,  such  a  modification  cannot  have  been 
caused  by  natural  selection.  I  will  consider  these  two 
points  separately. 

First  as  to  the  premiss,  it  is  not  true  that  every 
modification  of  structure  must  necessarily  be  function- 
less  when  it  first  begins  to  appear.  There  are  two 
very  good  reasons  why  such  should  not  be  the  case  in 
all  instances,  even  if  it  should  be  the  case  in  some. 
For,  as  a  matter  of  observable  fact,  a  very  large 
proportional  number  of  incipient  organs  are  useful 
from  the  very  moment  of  their  inception.  Take,  for 
example,  what  is  perhaps  the  most  wonderful  instance 
of  refined  mechanism  in  nature— the  eye  of  a  verte- 
brated  animal.  Comparative  anatomy  and  embryology 
combine  to  testify  that  this  organ  had  its  origin  in 
modifications  of  the  endings  of  the  ordinary  nerves 
of  the  skin.  Now  it  is  evident  that  from  the  very 
first  any  modification  of  a  cutaneous  nerve  whereby  it 
was  rendered  able,  in  however  small  a  degree,  to  be 
differently  affected  by  light  and  by  darkness  would  be 
of  benefit  to  the  creature  presenting  it ;  for  the 
creature  would  thus  be  able  to  seek  the  one  and  shun 
the  other  according  to  the  requirements  of  its  life. 


Criticisms  of  Theory  of  Natural  Selection.  353 

And  being  thus  useful  from  the  very  moment  of  its 
inception,  it  would  afterwards  be  gradually  improved 
as  variations  of  more  and  more  utility  presented  them- 
selves, until  not  only  would  finer  and  finer  degrees  of 
difference  between  light  and  shade  become  perceptible, 
but  even  the  outlines  of  solid  bodies  would  begin  to 
be  appreciated.  And  so  on,  stage  by  stage,  till  from 
an  ordinary  nerve-ending  in  the  skin  is  evolved  the 
eye  of  an  eagle. 

Moreover,  in  this  particular  instance  there  is  very 
good  reason  to  suppose  that  the  modification  of  the 
cutaneous  nerves  in  question  began  by  a  progressive 
increase  in  their  sensitiveness  to  temperature.  Wher- 
ever dark  pigment  happened  to  be  deposited  in  the 
skin — and  we  know  that  in  all  animals  it  is  apt  to  be 
deposited  in  points  and  patches,  as  it  were  by  accident, 
or  without  any  "prophecy"  as  to  future  uses,— the 
cutaneous  nerves  in  its  vicinity  would  be  better  able 
to  appreciate  the  difference  between  sun  and  shade  in 
respect  of  temperature,  even  though  as  yet  there  were 
no  change  at  all  in  these  cutaneous  nei  ves  tending  to 
make  them  responsive  to  light.  Now  it  is  easy  to  see 
how,  from  such  a  purely  accidental  beginning,  natural 
selection  would  have  had  from  the  first  sufficient 
material  to  act  upon.  It  being  of  advantage  to  a 
lowly  creature  that  it  should  distinguish  with  more 
and  more  delicacy,  or  with  more  and  more  rapidity, 
between  light  and  darkness  by  means  of  its  thermal 
sensations,  the  pigment  spots  in  the  skin  would  be 
rendered  permanent  by  natural  selection,  while  the 
nerves  in  that  region  would  by  the  same  agency 
be  rendered  more  and  more  specialized  as  organs 
adapted  to  perceive  changes  of  temperature,  until 

*  A  a 


354          Darwin^  and  after  Larwin. 

from  the  stage  of  responding  to  the  thermal  rays 
of  the  non-luminous  spectrum  alone,  they  become 
capable  of  responding  also  to  luminous. 

So  much,  then,  for  the  first  consideration  which 
serves  to  invalidate  the  Duke's  premiss.  The  second 
consideration  is,  that  very  often  an  organ  which  began 
by  being  useful  for  the  performance  of  one  function, 
after  having  been  fully  developed  for  the  performance 
of  that  function,  finds  itself,  so  to  speak,  accidentally 
fitted  to  the  performance  of  some  other  and  even  more 
important  function,  which  it  thereupon  begins  to 
discharge,  and  so  to  undergo  a  new  course  of  adaptive 
development.  In  such  cases,  and  so  far  as  the  new 
function  is  concerned,  the  difficulty  touching  the  first 
inception  of  an  organ  does  not  apply ;  for  here  the 
organ  has  already  been  built  up  by  natural  selection 
for  one  purpose,  before  it  begins  to  discharge  the 
other.  As  an  example  of  such  a  case  we  may  take 
the  lung  of  an  air-breathing  animal.  Originally  the 
lung  was  a  swim-bladder,  or  float,  and  as  such  it  was 
of  use  to  the  aquatic  ancestors  of  terrestrial  animals. 
But  as  these  ancestors  gradually  became  more  and  more 
amphibious  in  their  habits,  the  swim-bladder  began 
more  and  more  to  discharge  the  function  of  a  lung, 
and  so  to  take  a  wholly  new  point  of  departure  as 
regards  its  developmental  history.  But  clearly  there 
is  here  no  difficulty  with  regard  to  the  inception  of  its 
new  function,  because  the  organ  was  already  well 
developed  for  one  purpose  before  it  began  to  serve 
another.  Or,  to  take  only  one  additional  example, 
there  are  few  structures  in  the  animal  kingdom  so 
remarkable  in  respect  of  adaptation  as  is  the  wing  of 
a  bird  or  a  bat ;  and  at  first  sight  it  might  well  appear 


Criticisms  of  Theory  of  Natural  Selection.  355 

that  a  wing  could  be  of  no  conceivable  use  until  it  had 
already  acquired  enormous  proportional  dimensions, 
as  well  as  an  immense  amount  of  special  elaboration 
as  to  its  general  form,  size  of  muscle,  amount  of  blood- 
supply,  and  so  on.  For,  obviously,  not  until  it  had 
attained  all  these  things  could  it  even  begin  to  raise 
the  animal  in  the  air.  But  observe  how  fallacious  is 
this  argument.  Although  it  is  perfectly  true  that  a 
wing  could  be  of  no  use  as  a  wing  until  sufficiently 
developed  to  serve  the  purpose  of  flight,  this  is  merely 
to  say  that  until  it  has  become  a  wing  it  is  no  use  as 
a  wing.  It  does  not,  however,  follow  that  on  this 
account  it  was  of  no  prior  use  for  any  other  purpose. 
The  first  modifications  of  the  fore-limb  which  ended 
in  its  becoming  an  organ  of  flight  may  very  well  have 
been  due  to  adapting  it  as  an  organ  for  increased 
rapidity  of  locomotion  of  other  kinds — whether  on 
land  as  in  the  case  of  its  now  degenerated  form  in  the 
ostrich,  or  in  water  as  in  the  case  of  the  expanded  fins 
of  fish.  Indeed,  we  may  see  the  actual  process  of 
transition  from  the  one  function  to  the  other  in  the 
case  of  "  flying-fish."  Here  the  progressive  expansion 
of  the  pectoral  fins  must  certainly  have  been  always 
of  use  for  continuously  promoting  rapidity  of  loco- 
motion through  water  ;  and  thus  natural  selection 
may  have  continuously  increased  their  development 
until  they  now  begin  to  serve  also  as  wings  for  carry- 
ing the  animal  a  short  distance  through  air.  Again, 
in  the  case  of  the  so-called  flying  squirrels  we  find  the 
limbs  united  to  the  body  by  means  of  large  extensions 
of  the  skin,  so  that  when  jumping  from  one  tree  to 
another  the  animal  is  able  to  sustain  itself  through  a 
long  distance  in  the  air  by  merely  spreading  out  its 
A  a  2 


356          Darwin,  and  after  Darwin. 

limbs,  and  thus  allowing  the  skin-extensions  to  act 
after  the  manner  of  a  parachute.  Here,  of  course,  we 
have  not  yet  got  a  wing,  any  more  than  we  have  in 
the  case  of  the  flying-fish  ;  but  we  have  the  founda- 
tions laid  for  the  possible  development  of  a  future  wing, 
upon  a  somewhat  similar  plan  as  that  which  has  been 
so  wonderfully  perfected  in  the  case  of  bats.  And 
through  all  the  stages  of  progressive  expansion  which 
the  skin  of  the  squirrel  has  undergone,  the  expansion 
has  been  of  use,  even  though  it  has  not  yet  so  much 
as  begun  to  acquire  the  distinctive  functions  of  a  wing. 
Here,  then,  there  is  obviously  nothing  "  prophetic  "  in 
the  matter,  any  more  than  there  was  in  the  case  of  the 
swim-bladder  and  the  lung,  or  in  that  of  the  nerve- 
ending  and  the  eye.  In  short,  it  is  the  business  of 
natural  selection  to  secure  the  highest  available  degree 
of  adaptation  for  the  time  being ;  and,  in  doing  this, 
it  not  unfrequently  happens  that  an  extreme  develop- 
ment of  a  structure  in  one  direction  (produced  by 
natural  selection  for  the  sake  of  better  and  better 
adapting  the  structure  to  perform  some  particular 
function)  ends  by  beginning  to  adapt  it  to  the  perform- 
ance of  some  other  function.  And,  whenever  this 
happens  to  be  the  case,  natural  selection  forthwith 
begins  to  act  upon  the  structure,  so  to  speak,  from  a 
new  point  of  departure. 

So  much,  then,  for  the  Duke's  premiss — namely, 
that  "  every  modification  of  structure  must  have  been 
functionless  at  first,  when  it  began  to  appear."  This 
premiss  is  clearly  opposed  to  observable  fact.  But 
now,  the  second  position  is  that,  even  if  this  were  not 
so,  the  Duke's  conclusion  would  not  follow.  This 
conclusion,  it  will  be  remembered,  is,  that  if  incipient 


Criticisms  of  Theory  of  Natural  Selection.  357 

structures  are  useless,  it  necessarily  follows  that  natural 
selection  can  have  had  no  part  whatever  in  their 
inception.  Now,  this  is  a  conclusion  which  does  not 
"  necessarily  "  follow.  Even  if  it  be  granted  that  there 
are  structures  which  in  their  first  beginnings  are  not 
of  any  use  at  all  for  any  purpose,  it  is  still  possible 
that  they  may  owe  their  origin  to  natural  selection — 
not  indeed  directly,  but  indirectly.  This  possibility 
arises  from  the  occurrence  in  nature  of  a  principle 
which  has  been  called  the  Correlation  of  Growth. 

Mr.  Darwin,  who  has  paid  more  attention  to  this 
matter  than  any  other  writer,  has  shown,  in  consider- 
able detail,  that  all  the  parts  of  any  given  organism 
are  so  intimately  bound  together,  or  so  mutually 
dependent  upon  each  other,  that  when  one  part  is 
caused  to  change  by  means  of  natural  selection,  some 
other  parts  are  very  likely  to  undergo  modification  as 
a  consequence.  For  example,  there  are  several  kinds 
of  domesticated  pigeons  and  fowls,  which  grow  peculiar 
wing-like  feathers  on  the  feet.  These  are  quite  unlike 
all  the  other  feathers  in  the  animal,  except  those  of 
the  wing,  to  which  they  bear  a  very  remarkable  re- 
semblance. Mr.  Darwin  records  the  case  of  a  bantam 
where  these  wing-like  feathers  were  nine  inches  in 
length,  and  I  have  myself  seen  a  pigeon  where  they 
reproduced  upon  the  feet  a  close  imitation  of  the 
different  kinds  of  feathers  which  occupy  homologous 
positions  in  the  wing — primaries,  secondaries,  and 
tertiaries  all  being  distinctly  repeated  in  their  proper 
anatomical  relations.  Furthermore,  in  this  case, 
as  in  most  cases  where  such  wing-feathers  occur 
upon  the  feet,  the  third  and  fourth  toes  were  partly 
united  by  skin ;  and,  as  is  well  known,  in  the  wing 


358          Darwin,  and  after  Darwin. 

of  a  bird  the  third  and  fourth  digits  are  completely 
united  by  skin;  "so  that  in  feather-footed  pigeons, 
not  only  does  the  exterior  surface  support  a  row  of 
long  feathers,  like  wing-feathers  [which,  as  just  stated, 
may  in  some  cases  be  obviously  differentiated  into 
primaries,  secondaries  and  tertiaries],  but  the  very 
same  digits  which  in  the  wing  are  completely  united 
by  skin  become  partially  united  by  skin  in  the  feet ; 
and  thus  by  the  law  of  correlated  variation  of  homo- 
logous parts,  we  can  understand  the  curious  connexion 
of  feathered  legs  and  membrane  between  the  two  outer 
toes1."  The  illustration  is  drawn  from  the  specimen 
to  which  I  have  referred. 

Many  similar  instances  of  the  same  law  are  to  be 
met  with  throughout  organic  nature  ;  and  it  is  evident 
that  in  this  principle  we  find  a  conceivable  explanation 
of  the  origin  of  such  adaptive  structures  as  could  not 
have  been  originated  by  natural  selection  acting  directly 
upon  themselves  :  they  may  have  been  originated  by 
natural  selection  developing  other  adaptive  structures 
elsewhere  in  the  organism,  the  gradual  evolution  of 
which  has  entailed  the  production  of  these  by  correla- 
tion of  growth.  And,  if  so,  when  once  started  in  this 
way,  these  structures,  because  thus  accidentally  useful, 
will  now  themselves  come  under  the  direct  action  of 
natural  selection,  and  so  have  their  further  evolution 
determined  with  or  without  the  correlated  association 
which  first  led  to  their  inception. 

Of  course  it  must  be  understood  that  in  thus  apply- 
ing the  principle  of  correlated  growth,  to  explain  the 
origin  of  adaptive  structures  where  it  is  impossible  to 
explain  such  origin  by  natural  selection  having  from 

1   Variation  of  Plants  and  Animals,  vol.  ii.  p.  315. 


Criticisms  of  Theory  of  Natural  Selection.  359 

the  first  acted  directly  upon  these  structures  them- 
selves, Darwinists  do  not  suppose  that  in  all — or  even 
in  most — cases  of  correlated  growth  the  correlated 
structures  are  of  use.  On  the  contrary,  it  is  well 
known  that  structures  due  to  correlated  growth  are, 


FlG.  117.— Feather-footed  pigeon.    Drawn  from  nature. 

as  a  rule,  useless.  Being  only  the  by-products  of 
adaptive  changes  going  on  elsewhere,  in  any  given 
case  the  chances  are  against  these  correlated  effects 
being  themselves  of  any  utilitarian  significance ;  and, 
therefore,  as  a  matter  of  fact,  correlated  growths 
appear  to  be  usually  meaningless  from  the  point  of 


360          Darwin,  and  after  Darwin. 

view  of  adaptation.  Still,  on  the  doctrine  of  chances, 
it  is  to  be  expected  that  sometimes  a  change  of 
structure  which  has  thus  been  indirectly  produced  by 
correlation  of  growth  might  happen  to  prove  useful 
for  some  purpose  or  another ;  and  in  as  many  cases 
as  such  indirectly  produced  structures  do  prove  useful, 
they  will  straightway  begin  to  be  improved  by  the 
direct  action  of  natural  selection.  In  all  such  cases, 
therefore,  we  should  have  an  explanation  of  the  origin 
of  such  a  structure,  which  is  the  only  point  that  we 
are  now  considering. 

I  think,  then,  that  all  this  effectually  disposes  of 
the  doctrine  of  "prophetic  germs."  But,  before 
leaving  the  subject,  I  should  like  to  make  one 
further  statement  of  greater  generality  than  any  which 
I  have  hitherto  advanced.  This  statement  is,  that  we 
must  remember  how  large  a  stock  of  meaningless 
structures  are  always  being  produced  in  the  course  of 
specific  transmutations,  not  only  by  correlation  of 
growth,  which  we  have  just  been  considering,  but  also 
by  the  direct  action  of  external  conditions,  together 
with  the  constant  play  of  all  the  many  and  complex 
forces  internal  to  organisms  themselves.  In  other 
words,  important  as  the  principle  of  correlation 
undoubtedly  is,  we  must  remember  that  even  this  is 
very  far  from  being  the  only  principle  which  is  con- 
cerned in  the  origination  of  structures  that  may  or  may 
not  chance  to  be  useful.  Therefore,  it  is  not  only 
natural  selection  when  operating  indirectly  through 
the  correlation  of  growth  that  is  competent  to  produce 
new  structures  without  reference  to  utility.  In  all 
the  complex  action  and  reaction  of  internal  and  ex- 
ternal forces,  new  variations  are  perpetually  arising 


Criticisms  of  Theory  of  Natural  Selection.  361 

without  any  reference  to  utility,  either  present  or 
future.  Among  all  this  multitude  of  promiscuous 
variations,  the  chances  must  be  that  some  percentage 
will  prove  of  some  service,  either  from  the  first  moment 
of  their  appearance,  or  else  after  they  have  undergone 
some  amount  of  development.  Such  development 
prior  to  utility  may  be  due,  either  to  correlation  of 
growth,  to  the  structure  having  previously  performed 
some  other  function,  as  already  explained,  or  else  to 
a  continued  operation  of  the  causes  which  were  con- 
cerned in  the  first  appearance  of  originally  useless 
characters.  In  a  series  of  chapters  which  will  be 
devoted  to  the  whole  question  of  utility  in  the  next 
volume,  I  shall  hope  to  give  very  good  reasons  for 
concluding  that  useless  characters  are  not  only  of 
highly  frequent  occurrence,  but  are  due  to  a  variety  of 
other  causes  besides  correlation  of  growth.  And,  if  so, 
the  possibility  of  originally  useless  characters  happen- 
ing in  some  cases  to  become,  by  increased  develop- 
ment, useful  characters,  is  correspondingly  increased. 
Among  a  hundred  varietal  or  specific  characters  which 
are  directly  produced  in  as  many  different  species  by 
a  change  of  climate,  for  example,  some  five  or  six  may 
be  potentially  useful :  that  is  to  say,  characters  thus 
adventitiously  produced  in  an  incipient  form  may 
only  require  to  be  further  developed  by  a  continuance 
of  the  same  causes  as  first  originated  them,  in  order 
that  some  percentage  of  the  whole  number  shall  become 
of  some  degree  of  use.  Those  professed  followers  of 
Darwin,  therefore,  who  without  any  reason — or,  as  it 
appears  to  me,  against  all  reason — deny  the  pos- 
sibility of  useless  specific  characters  in  any  case  or 
in  any  degree  (unless  correlated  with  useful  characters), 


362  Darwin,  and  after  Darwin. 

are  playing  into  the  hands  of  Darwin's  critics  by 
indirectly  countenancing  the  difficulty  which  we  are 
now  considering.  For,  if  correlation  of  growth  is 
unreasonably  supposed  to  be  the  only  possible  cause 
of  the  origin  of  incipient  structures  which  are  not  use- 
ful from  the  first  moment  of  their  inception,  clearly 
the  field  is  greatly  narrowed  as  regards  the  occurrence 
of  incipient  characters  sufficient  in  amount— and,  still 
more,  in  constancy  of  appearance  and  persistency  of 
transmission—  to  admit  of  furnishing  material  for  the 
working  of  natural  selection.  But  in  the  measure  that 
incipient  characters — whether  varietal  or  specific — 
are  recognised  as  not  always  or  "necessarily"  useful 
from  the  moment  of  their  inception,  and  yet  capable  of 
being  developed  to  a  certain  extent  by  the  causes 
which  first  led  to  their  occurrence,  in  that  measure  is 
this  line  of  criticism  closed.  For  of  all  the  variations 
which  thus  occur,  it  is  only  those  which  afterwards 
prove  of  any  use  that  are  laid  hold  upon  and  wrought 
up  by  natural  selection  into  adaptive  structures,  or 
working  organs.  And,  therefore,  what  we  see  in 
organic  nature  is  the  net  outcome  of  the  development 
of  all  the  happy  chances.  So  it  comes  that  the 
appearance  presented  by  organic  nature  as  a  whole  is 
that  of  a  continual  fulfilment  of  structural  prophecies, 
when,  in  point  of  fact,  if  we  had  a  similar  record  of  all 
the  other  variations  it  would  be  seen  that  possibly 
not  one  such  prophecy  in  a  thousand  is  ever  destined 
to  be  fulfilled. 

Here,  then,  I  feel  justified  in  finally  taking  leave  of 
the  difficulty  from  the  uselessness  of  incipient  organs, 
as  this  difficulty  has  been  presented,  in  varying  degrees 


Criticisms  of  Theory  of  Natural  Selection.  363 

of  emphasis,  by  the  Duke  of  Argyll,  Mr.  Mivart,  Pro- 
fessors Nageli,  Bronn,  Broca,  Eimer,  and,  indeed,  by  all 
other  writers  who  have  hitherto  advanced  it.  For,  as 
thus  presented,  I  think  I  have  shown  that  it  admits  of 
being  adequately  met.  But  now,  I  must  confess,  to  me 
individually  it  does  appear  that  behind  this  erroneous 
presentation  of  the  difficulty  there  lies  another  question, 
which  is  deserving  of  much  more  serious  attention. 
For  although  it  admits  of  being  easily  shown — as  I  have 
just  shown — that  the  difficulty  as  ordinarily  presented 
fails  on  account  of  its  extravagance,  the  question 
remains  whether,  if  stated  with  more  moderation,  a 
real  difficulty  might  not  be  found  to  remain. 

My  quarrel  with  the  conclusion,  like  my  quarrel 
with  the  premiss,  is  due  to  its  universality.  By  say- 
ing in  the  premiss  that  all  incipient  organs  are  neces- 
sarily useless  at  the  time  of  their  inception,  these 
writers  admit  of  being  controverted  by  fact ;  and  by 
saying  in  the  conclusion  that,  if  all  incipient  organs 
are  useless,  it  necessarily  follows  that  in  no  case  can 
natural  selection  have  been  the  cause  of  building  up 
an  organ  until  it  becomes  useful,  they  admit  of  being 
controverted  by  logic.  For,  even  if  the  premiss  were 
true  in  fact — namely,  that  all  incipient  organs  are  use- 
less at  the  time  of  their  inception, — it  would  not 
necessarily  follow  that  in  no  case  could  natural  selec- 
tion build  up  a  useless  structure  into  a  useful  one ; 
because,  although  it  is  true  that  in  no  case  can  natural 
selection  do  this  by  acting  on  a  useless  structure 
directly,  it  may  do  so  by  acting  on  the  useless  struc- 
ture indirectly,  through  its  direct  action  on  some  other 
part  of  the  organism  with  which  the  useless  structure 
happens  to  be  correlated.  Moreover,  as  I  believe,  and 


364          Darwin,  and  after  Darwin. 

will  subsequently  endeavour  to  prove,  there  is  abun- 
dant evidence  to  show  that  incipient  characters  are 
often  developed  to  a  large  extent  by  causes  other 
than  natural  selection  (or  apart  from  any  reference  to 
utility),  with  the  result  that  some  of  them  thus  happen 
to  become  of  use,  when,  of  course,  the  supposed  diffi- 
culty is  at  an  end. 

But  although  it  is  thus  easy  to  dispose  of  both  the 
propositions  in  question,  on  account  of  their  univer- 
sality, stated  more  carefully  they  would  require,  as 
I  have  said,  more  careful  consideration.  Thus,  if  it 
had  been  said  that  some  incipient  organs  are  presum- 
ably useless  at  the  time  of  their  inception,  and  that  in 
some  of  these  cases  it  is  difficult,  or  impossible,  to  con- 
ceive how  the  principle  of  correlation,  or  any  other 
principle  hitherto  suggested,  can  apply— then  the 
question  would  have  been  raised  from  the  sphere  of 
logical  discussion  to  that  of  biological  fact.  And 
the  new  question  thus  raised  would  have  to  be  de- 
bated, no  longer  on  the  ground  of  general  or  abstract 
principles,  but  on  that  of  special  or  concrete  cases. 
Now  until  within  the  last  year  or  two  it  has  not  been 
easy  to  find  such  a  special  or  concrete  case — that  is  to 
say,  a  case  which  can  be  pointed  to  as  apparently 
excluding  the  possibility  of  natural  selection  having 
had  anything  to  do  with  the  genesis  of  an  unquestion- 
ably adaptive  structure.  But  eventually  such  a  case 
has  arisen,  and  the  Duke  of  Argyll  has  not  been  slow 
in  perceiving  its  importance.  This  case  is  the  electric 
organ  in  the  tail  of  the  skate.  No  sooner  had  Pro- 
fessor Cossar  Ewart  published  an  abstract  of  his  first 
paper  on  this  subject,  than  the  Duke  seized  upon  it  as 
a  case  for  which,  as  he  said,  he  had  long  been  waiting 


Criticisms  of  Theory  of  Natural  Selection.  365 

— namely,  the  case  of  an  adaptive  organ  the  genesis  of 
which  conld  not  possibly  be  attributed  to  natural  selec- 
tion, and  must  therefore  be  attributed  to  supernatural 
design.  Now,  I  do  not  deny  that  he  is  here  in  pos- 
session of  an  admirable  case — a  case,  indeed,  so  ad- 
mirable that  it  almost  seems  to  have  been  specially 
designed  for  the  discomfiture  of  Darwinians.  There- 
fore, in  order  to  do  it  full  justice,  I  will  show  that  it  is 
even  more  formidable  than  the  Duke  of  Argyll  has 
represented. 

Electric  organs  are  known  to  occur  in  several  widely 
different  kinds  of  fish — such  as  the  Gymnotus  and 
Torpedo.  Wherever  these  organs  do  occur,  they 
perform  the  function  of  electric  batteries  in  storing 
and  discharging  electricity  in  the  form  of  more  or  less 
powerful  shocks.  Here,  then,  we  have  a  function 
which  is  of  obvious  use  to  the  fish  for  purposes  both 
of  offence  and  defence.  These  organs  are  everywhere 
composed  of  a  transformation  of  muscular,  together 
with  an  enormous  development  of  nervous  tissue ; 
but  inasmuch  as  they  occupy  different  positions,  and 
are  also  in  other  respects  dissimilar  in  the  different 
zoological  groups  of  fishes  where  they  occur,  no  diffi- 
culty can  be  alleged  as  to  these  analogous  organs 
being  likewise  homologous  in  different  divisions  of  the 
aquatic  vertebrata. 

Now,  in  the  particular  case  of  the  skate,  the  organ 
is  situated  in  the  tail,  where  it  is  of  a  spindle-like 
form,  measuring,  in  a  large  fish,  about  two  feet  in 
length  by  about  an  inch  in  diameter  at  the  middle  of 
the  spindle.  Although  its  structure  is  throughout 
as  complex  and  perfect  as  that  of  the  electric  organ  in 
Gymnotus  or  Torpedo,  its  smaller  size  does  not  admit 


366          Darwin,  and  after  Darwin. 

of  its  generating  a  sufficient  amount  of  electricity 
to  yield  a  discharge  that  can  be  felt  by  the  hand 
Nevertheless,  that  it  does  discharge  under  suitable 
stimulation  has  been  proved  by  Professor  Burdon 
Sanderson  by  means  of  a  telephone  ;  for  he  found 
that  every  time  he  stimulated  the  animal  its  electrical 
discharge  was  rendered  audible  by  the  telephone. 
Here,  then,  the  difficulty  arises.  For  of  what  conceiv- 
able use  is  such  an  organ  to  its  possessor  ?  We  can 
scarcely  suppose  that  "any  aquatic  animal  is  more 
sensitive  to  electric  shocks  than  is  the  human  hand  ; 
and  even  if  such  were  the  case,  a  discharge  of  so  feeble 
a  kind  taking  place  in  water  would  be  short-cir- 
cuited in  the  immediate  vicinity  of  the  skate  itself. 
So  there  can  be  no  doubt  that  such  weak  discharges 
as  the  skate  is  able  to  deliver  must  be  wholly  imper- 
ceptible alike  to  prey  and  to  enemies.  Yet  for  the 
delivery  of  such  discharges  there  is  provided  an  organ 
of  such  high  peculiarity  and  huge  complexity,  that, 
regarded  as  a  piece  of  living  mechanism,  it  deserves  to 
rank  as  at  once  the  most  extremely  specialized  and 
the  most  highly  elaborated  structure  in  the  whole 
animal  kingdom.  Thousands  of  separately  formed 
elements  are  ranged  in  row  after  row,  all  electrically 
insulated  one  from  another,  and  packed  away  into  the 
smallest  possible  space,  with  the  obvious  end,  or 
purpose,  of  conspiring  together  for  the  simultaneous 
delivery  of  an  electric  shock.  Nevertheless,  the  shock 
when  delivered  is,  as  we  have  just  seen,  too  slight  to 
be  of  any  conceivable  use  to  the  skate.  Therefore  it 
appears  impossible  to  suggest  how  this  astonishing 
structure — much  more  astonishing,  in  my  opinion, 
than  the  human  eye  or  the  human  hand — can  ever 


Criticisms  of  Theory  of  Natural  Selection.  367 

have  been  begun,  or  afterwards  developed,  by  means 
of  natural  selection.  For  if  it  be  not  even  yet  of  any 
conceivable  use  to  its  possessor,  clearly  thus  far  sur- 
vival of  the  fittest  can  have  had  nothing  to  do  with  its 
formation.  On  the  other  hand,  seeing  that  electric 
organs  when  of  larger  size,  as  in  the  Gymnotus  and 
Torpedo,  are  of  obvious  use  to  their  possessors,  the 
facts  of  the  case,  so  far  as  the  skate  is  concerned, 
assuredly  do  appear  to  sanction  the  doctrine  of  "  pro- 
phetic germs/'  The  organ  in  the  skate  seems  to  be  on 
its  way  towards  becoming  such  an  organ  as  we  meet 
with  in  these  other  animals  ;  and,  therefore,  unless  we 
can  show  that  it  is  now,  and  in  all  previous  stages  of 
its  evolution  has  throughout  been,  of  use  to  the  skate, 
the  facts  do  present  a  serious  difficulty  to  the  theory 
of  natural  selection,  while  they  readily  lend  themselves 
to  the  interpretation  of  a  disposing  or  fore-ordaining 
mind,  which  knows  how  to  construct  an  electric  bat- 
tery by  thus  transforming  muscular  tissue  into  electric 
tissue,  and  is  now  actually  in  process  of  constructing 
such  an  apparatus  for  the  prospective  benefit  of  future 
creatures. 

Should  it  be  suggested  that  possibly  the  electric 
organ  of  the  skate  may  be  in  process  of  degeneration, 
and  therefore  that  it  is  now  the  practically  function- 
less  remnant  of  an  organ  which  in  the  ancestors  of 
the  skate  was  of  larger  size  and  functional  use — against 
so  obvious  a  suggestion  there  lie  the  whole  results  of 
Professor  Ewart's  investigations,  which  go  to  indicate 
that  the  organ  is  here  not  in  a  stage  of  degeneration, 
but  of  evolution.  For  instance,  in  Raia  radiata,  it  does 
not  begin  to  be  formed  out  of  the  muscular  tissue  until 
some  time  after  the  animal  has  left  the  egg-capsule, 


368          Darwin,  and  after  Darwin. 

and  assumed  all  the  normal  proportions  (though 
not  yet  the  size)  of  the  adult  creature.  The  organ, 
therefore,  is  one  of  the  very  latest  to  appear  in  the 
ontogeny  of  R.  radiata ;  and,  moreover,  it  does  not 
attain  its  full  development  (i.  e.  not  merely  growth,  but 


FIG.  1 18. — Raia  radiata,  representing  the  liie  size  of  the  youngest  in- 
dividual in  which  muscle  fibres  have  been  found  developing  into  electric 
cells. 

transforming  of  muscular  fibres  into  electrical  ele- 
ments) till  the  fish  attains  maturity.  Read  in  the 
light  of  embryology,  these  facts  prove,  (i)  that  the 
electric  organ  of  R.  radiata  must  be  one  of  the  very 


FIG.  1 19.— Electric  organ  of  the  Skate.  The  left-hand  drawing  (I)  represents  the 
entire  organ  (natural  size)  of  a  fuli-grown  /?.  radiata.  This  is  a  small  skate,  which 
rarely  exceeds  50  centms.  in  length ;  but  in  the  large  R.  balis,  the  organ  may 
exceed  two  feet  in  length.  The  other  drawings  represent  single  muscle-fibres  in  suc- 
cessive stages  of  transition.  In  the  first  of  the  series  (II)  the  motor  plate,  and  the  nerves 
connected  with  it,  have  already  been  considerably  enlarged.  In  the  other  three  specimens, 
the  fibre  becomes  more  and  more  club-like,  and  eventually  cup-like.  These  changes 
of  shape  are  expressive  of  great  changes  of  structure,  as  may  be  seen  in  the  last 


of   the    series  (V),   where    the   shallow 


plate  lines  the  concavity  of  the  cup,  and  is  richly  si 
which  are  represented  in  the  last  drawing) :  the  thic 
muscular  fibres,  the  striation  of  which  is  distinctly  visi 

b 


is  seen  in  partial  section.  The  electric 
supplied  with  nerves  (only  a  few  of 
'  -k  walls  of  the  cup  are  composed  of 
'ble. 


370          Darwin,  and  after  Darwin. 

latest  products  of  the  animal's  phylogeny  ;  and,  (2) 
that  as  yet.  at  all  events,  it  has  not  begun  to  degenerate. 
But,  if  not,  it  must  either  be  at  a  stand-still,  or  it  must 
be  in  course  of  further  evolution  ;  and,  whichever  of 


FlG.  1 20. — Electric  cells  of  Kaia  radiata.  The  drawing  on  the  left 
represents  one  of  the  clubs  magnified,  as  in  the  preceding  wood-cut. 
The  drawing  on  the  right  represents  a  number  of  these  clubs,  less  highly 
magnified,  in  situ. 

these  alternatives  we  adopt,  the  difficulty  of  account- 
ing for  its  present  condition  remains.  In  this  con- 
nexion also  it  is  worth  while  to  remark  that  the  electric 


Criticisms  of  Theory  of  Natural  Selection.  371 

organ,  even  after  it  has  attained  its  full  development, 
continues  \\sgrowth  with  the  growth  of  the  fish,  and 
this  in  a  much  higher  ratio,  either  than  the  tail  alone, 
or  the  whole  animal.  Lastly,  Prof.  Burdon  Sanderson 
finds  that  section  for  section  the  organ  in  the  skate  is 
as  efficient  as  it  is  in  Torpedo.  It  is  evident  that 
these  facts  also  point  to  the  skate's  organ  being  in 
course  of  phylogenetic  evolution. 

Again,  it  cannot  be  answered  that  the  principle 
of  correlation  may  be  drawn  upon  in  mitigation  of 
the  difficulty.  The  structure  of  the  electric  organ 
is  far  too  elaborate,  far  too  specialized,  and  far  too 
obviously  directed  to  a  particular  end,  to  admit  of  our 
conceivably  supposing  it  due  to  any  accidental  corre- 
lation with  structural  changes  going  on  elsewhere. 
Even  as  regards  the  initial  changes  of  muscle-elements 
into  electrical-elements,  I  do  not  think  the  principle 
of  correlation  can  be  reasonably  adduced  by  way 
of  explanation ;  for,  as  shown  in  the  illustrations, 
even  this  initial  change  is  most  extraordinarily 
peculiar,  elaborate,  and  specialized.  But,  be  this  as 
it  may,  I  am  perfectly  certain  that  the  principle  of 
correlation  cannot  possibly  be  adduced  to  explain  the 
subsequent  association  of  these  electrical  elements  into 
an  electric  battery,  actuated  by  a  special  nervous  me- 
chanism of  enormous  size  and  elaboration — unless,  of 
course,  the  progress  of  such  a  structure  were  assumed 
to  have  been  throughout  of  some  utility.  Under  this 
supposition,  however,  the  principle  of  correlation  would 
be  forsaken  in  favour  of  that  of  natural  selection  ;  and 
we  should  again  be  in  the  presence  of  the  same  diffi- 
culty as  that  with  which  we  started. 

But  now,  and  further,  if  we  do  thus  abandon  corre- 
B  b  2 


372          Darwin,  and  after  Darwin. 

lation  in  favour  of  natural  selection,  and  therefore  if 
for  the  sake  of  saving  an  hypothesis  we  assume  that 
the  organ  as  it  now  stands  must  be  of  some  use  to  the 
existing  skate,  we  should  still  have  to  face  the  question 
— Of  what  conceivable  use  can  those  initial  stages  of  its 
formation  have  been,  when  first  the  muscle-elements 
began  to  be  changed  into  the  very  different  electrical- 
elements,  and  when  therefore  they  became  useless  as 
muscles  while  not  yet  capable  of  performing  even  so 
much  of  the  electrical  function  as  they  now  perform  ? 
Lastly,  we  must  remember  that  not  only  have  we 
here  the  most  highly  specialized,  the  most  complex, 
and  altogether  the  most  elaboratively  adaptive  organ 
in  the  animal  kingdom  ;  but  also  that  in  the  formation 
of  this  structure  there  has  been  needed  an  altogether 
unparalleled  expenditure  of  the  most  physiologically 
expensive  of  all  materials—  namely,  nervous  tissue. 
Whether  estimated  by  volume  or  by  weight,  the 
quantity  of  nervous  tissue  which  is  consumed  in  the 
electric  organ  of  the  skate  is  in  excess  of  all  the  rest 
of  the  nervous  system  put  together.  It  is  need- 
less to  say  that  nowhere  else  in  the  animal  king- 
dom— except,  of  course,  in  other  electric  fishes — is 
there  any  approach  to  so  enormous  a  development  of 
nervous  tissue  for  the  discharge  of  a  special  function. 
Therefore,  as  nervous  tissue  is,  physiologically  speak- 
ing, the  most  valuable  of  all  materials,  we  are  forced 
to  conclude  that  natural  selection  ought  strongly  to 
have  opposed  the  evolution  of  such  organs,  unless  from 
the  first  moment  of  their  inception,  and  throughout  the 
whole  course  of  their  development,  they  were  of  some 
such  paramount  importance  as  biologically  to  justify  so 
unexampled  an  expenditure.  Yet  this  paramount  im- 


Criticisms  of  Theory  of  Natural  Selection.   373 

portance  does  not  admit  of  being  so  much  as  surmised, 
even  where  the  organ  has  already  attained  the  size  and 
degree  of  elaboration  which  it  presents  in  the  skate. 

In  view  of  all  these  considerations  taken  together, 
I  freely  confess  that  the  difficulty  presented  by  this 
case  appears  to  me  of  a  magnitude  and  importance 
altogether  unequalled  by  that  of  any  other  single  case 
— or  any  series  of  cases — which  has  hitherto  been  en- 
countered by  the  theory  of  natural  selection.  So  that, 
if  there  were  many  other  cases  of  the  like  kind  to  be 
met  with  in  nature,  I  should  myself  at  once  allow  that 
the  theory  of  natural  selection  would  have  to  be  dis- 
carded. But  inasmuch  as  this  particular  case  stands 
so  far  entirely  by  itself,  and  therefore  out  of  analogy 
with  thousands,  or  even  millions,  of  other  cases 
throughout  the  whole  range  of  organic  nature,  I  am 
constrained  to  feel  it  more  probable  that  the  electric 
organ  of  the  skate  will  some  day  admit  of  being  mar- 
shalled under  the  general  law  of  natural  selection — in 
just  the  same  way  as  proved  to  be  the  case  with  the 
conspicuous  colouring  of  those  caterpillars,  which,  as 
explained  in  the  last  chapter,  at  one  time  seemed  to 
constitute  a  serious  difficulty  to  the  theory,  and  yet, 
through  a  better  knowledge  of  all  the  relations  in- 
volved, has  now  come  to  constitute  one  of  the  strongest 
witnesses  in  its  favour. 

I  have  now  stated  all  the  objections  of  any  import- 
ance which  have  hitherto  been  brought  against  the 
theory  of  natural  selection,  excepting  three,  which  I 
left  to  be  dealt  with  together  because  they  form  a 
logically  connected  group.  With  a  brief  consideration 
of  these,  therefore,  I  will  bring  this  chapter  to  a  close. 


374          Darwin,  and  after  Darwin. 

The  three  objections  to  which  I  allude  are,  (i)  that 
a  large  proportional  number  of  specific,  as  well  as 
of  higher  taxonomic  characters,  are  seemingly  useless 
characters,  and  therefore  do  not  lend  themselves  to 
explanation  by  the  Darwinian  theory;  (2)  that  the 
most  general  of  all  specific  characters — viz.  cross- 
infertility  between  allied  species — cannot  possibly 
be  due  to  natural  selection,  as  is  demonstrated  by 
Darwin  himself;  (3)  that  the  swamping  effects  of 
free  intei  crossing  must  always  render  impossible  by 
natural  selection  alone  any  evolution  of  species  in 
divergent  (as  distinguished  from  serial)  lines  of 
change. 

These  three  objections  have  been  urged  from  time 
to  time  by  not  a  few  of  the  most  eminent  botanists 
and  zoologists  of  our  century ;  and  from  one  point 
of  view  I  cannot  myself  have  the  smallest  doubt  that 
the  objections  thus  advanced  are  not  only  valid  in 
themselves,  but  also  by  far  the  most  formidable 
objections  which  the  theory  of  natural  selection  has 
encountered.  From  another  point  of  view,  however, 
I  am  equally  convinced  that  they  all  admit  of  ab- 
solute annihilation.  This  strong  antithesis  arises,  as 
I  have  said,  from  differences  of  standpoint,  or  from 
differences  in  the  view  which  we  take  of  the  theory  of 
natural  selection  itself.  If  we  understand  this  theory 
to  set  forth  natural  selection  as  the  sole  cause  of 
organic  evolution,  then  all  the  above  objections  to  the 
theory  are  not  merely,  as  already  stated,  valid  and 
formidable,  but  as  I  will  now  add,  logically  insur- 
mountable. On  the  other  hand,  if  we  take  theory 
to  consist  merely  in  setting  forth  natural  selection  as 
a  factor  of  organic  evolution,  even  although  we  be- 


Criticisms  of  Theory  of  Natural  Selection.  375 

lieve  it  to  have  been  the  chief  factor  or  principal  cause, 
all  the  three  objections  in  question  necessarily  vanish. 
For  in  this  case,  even  if  it  be  satisfactorily  proved  that 
the  theory  of  natural  selection  is  unable  to  explain  the 
three  classes  of  facts  above  mentioned,  the  theory  is 
not  thereby  affected  :  facts  of  each  and  all  of  these 
classes  may  be  consistently  left  by  the  theory  to  be 
explained  by  causes  other  than  natural  selection — 
whether  these  be  so  far  capable  or  incapable  of 
hypothetical  formulation.  Thus  it  is  evident  that 
whether  the  three  objections  above  named  are  to 
be  regarded  as  logically  insurmountable  by  the 
theory,  or  as  logically  non-existent  in  respect  to  it, 
depends  simply  upon  the  manner  in  which  the  theory 
itself  is  stated. 

In  the  next  volume  a  great  deal  more  will  have  to 
be  said  upon  these  matters — especially  with  regard  to 
the  causes  other  than  natural  selection  which  in  my 
opinion  are  capable  of  explaining  these  so-called 
"  difficulties."  In  the  present  connexion,  however, 
all  I  have  attempted  to  show  is,  that,  whatever  may 
be  thought  touching  the  supplementary  theories 
whereby  I  shall  endeavour  to  explain  the  facts  of 
inutility,  cross-sterility,  and  non-occurrence  of  free 
intercrossing,  no  one  of  these  facts  is  entitled  to  rank 
as  an  objection  against  the  theory  of  natural  selection, 
unless  we  understand  this  theory  to  claim  an  ex- 
clusive prerogative  in  the  field  of  organic  evolution. 
This,  as  we  have  previously  seen,  is  what  Mr.  Wallace 
does  claim  for  it ;  while  on  the  other  hand,  Mr. 
Darwin  expressly — and  even  vehemently— repudiates 
the  claim  :  from  which  it  follows  that  all  the  three 
main  objections  against  the  theory  of  natural  selection 


376          Darwin,  and  after  Darwin. 

are  objections  which  vitally  affect  the  theory  only  as 
it  has  been  stated  and  upheld  by  Wallace.  As  the 
theory  has  been  stated  and  upheld  by  Darwin,  all 
these  objections  are  irrelevant.  This  is  a  fact  which 
I  had  not  myself  perceived  at  the  time  when  I  men- 
tioned these  objections  in  a  paper  entitled  Physio- 
logical Selection,  which  was  published  in  1886.  The 
discussions  to  which  that  paper  gave  rise,  however,  led 
me  to  consider  these  matters  more  closely ;  and 
further  study  of  Darwin's  writings,  with  these  matters 
specially  in  view,  has  led  me  to  see  that  none  of  the 
objections  in  question  are  relevant  to  his  theory,  as 
distinguished  from  that  of  Mr.  Wallace.  This,  I 
acknowledge,  I  ought  to  have  perceived  before  I 
published  the  paper  just  alluded  to  ;  but  in  those 
days  I  had  had  no  occasion  to  follow  out  the  dif- 
ferences between  Darwin  and  Wallace  to  all  their 
consequences,  and  therefore  adopted  the  prevalent 
view  that  their  theories  of  evolution  were  virtually 
identical.  Now,  however,  I  have  endeavoured  to 
make  it  clear  that  tiie  points  wherein  they  differ 
involve  the  important  consequences  above  set  forth. 
All  these  the  most  formidable  objections  against  the 
theory  of  natural  selection  arise  simply  and  solely 
from  what  I  conceive  to  be  the  erroneous  manner  in 
which  the  theory  has  been  presented  by  Darwin's 
distinguished  colleague. 

I  have  now  considered,  as  impartially  as  I  can,  all 
the  main  criticisms  and  objections  which  have  been 
brought  against  the  theory  of  natural  selection ;  and 
the  result  is  to  show  that,  neither  singly  nor  col- 
lectively, are  they  entitled  to  much  weight.  On  the 


Criticisms  of  Theory  of  Natural  Selection.  377 

other  hand,  as  we  have  seen  in  the  preceding  chapter, 
there  is  a  vast  accumulation  of  evidence  in  favour  of 
the  theory.  Hence,  it  is  no  wonder  that  the  theory 
has  now  been  accepted  by  all  naturalists,  with  scarcely 
any  one  notable  exception,  as  at  any  rate  the  best 
working  hypothesis  which  has  ever  been  propounded 
whereby  to  explain  the  facts  of  organic  evolution. 
Moreover,  in  the  opinion  of  those  most  competent  to 
judge,  the  theory  is  entitled  to  be  regarded  as  some- 
thing very  much  more  than  a  working  hypothesis : 
it  is  held  to  be  virtually  a  completed  induction,  or, 
in  other  words,  the  proved  exhibition  of  a  general 
law,  whereby  the  causation  of  organic  evolution  ad- 
mits of  being  in  large  part — if  not  altogether — 
explained. 

Now,  whether  or  not  we  subscribe  to  this  latter 
conclusion  ought,  I  think,  to  depend  upon  v/hat  we 
mean  by  an  explanation  in  the  case  which  is  before 
us.  If  we  mean  only  that,  given  the  large  class  of 
known  facts  and  unknown  causes  which  are  conveni- 
ently summarized  under  the  terms  Heredity  and 
Variability,  then  the  further  facts  of  Struggle  and 
Survival  serve,  in  some  considerable  degree  or 
another,  to  account  for  the  phenomena  of  adaptive 
evolution,  I  cannot  see  any  room  to  question  that 
the  evidence  is  sufficient  to  prove  the  statement 
But  it  is  clear  that  by  taking  for  granted  these  great 
facts  of  Heredity  and  Variability,  we  have  assumed 
the  larger  part  of  the  problem  as  a  whole.  Or,  more 
correctly,  by  thus  generalizing,  in  a  merely  verbal 
form,  all  the  unknown  causes  which  are  concerned  in 
these  two  great  factors  of  the  process  in  question,  we 
are  not  so  much  as  attempting  to  explain  the  pre- 


378          Darwin,  and  after  Darwin. 

cedent  causation  which  serves  as  a  condition  to  the 
process.  Much  more  than  half  the  battle  would 
already  have  been  won,  had  Darwin's  predecessors 
been  able  to  explain  the  causes  of  Heredity  and 
Variation ;  hence  it  is  but  a  very  partial  victory 
which  we  have  hitherto  gained  in  our  recent  discovery 
of  the  effects  of  Struggle  and  Survival. 

Yet  partial  though  it  be  in  relation  to  the  whole 
battle,  in  itself,  or  considered  absolutely,  there  can  be 
no  reasonable  doubt  that  it  constitutes  the  greatest 
single  victory  which  has  ever  been  gained  by  the 
science  of  Biology.  For  this  very  reason,  however, 
it  behoves  us  to  consider  all  the  more  carefully  the 
extent  to  which  it  goes.  But  my  discussion  of  this 
matter  must  be  relegated  to  the  next  volume,  where 
I  hope  to  give  abundant  proof  of  the  soundness  of 
Darwin's  judgment  as  conveyed  in  the  words : — "  I 
am  convinced  that  natural  selection  has  been  the  main, 
but  not  the  exclusive,  means  of  modification." 


CHAPTER  X. 

THE  THEORY  OF  SEXUAL  SELECTION,  AND 
CONCLUDING  REMARKS. 

ALTHOUGH  the  explanatory  value  of  the  Darwinian 
theory  of  natural  selection  is,  as  we  have  now  seen, 
incalculably  great,  it  nevertheless  does  not  meet  those 
phenomena  of  organic  nature  which  perhaps  more 
than  any  other  attract  the  general  attention,  as  well 
as  the  general  admiration,  of  mankind  :  I  mean  all 
that  class  of  phenomena  which  go  to  constitute  the 
Beautiful.  Whatever  value  beauty  as  such  may  have, 
it  clearly  has  not  a  life-preserving  value.  The  gorgeous 
plumage  of  a  peacock,  for  instance,  is  of  no  advantage 
to  the  peacock  in  his  struggle  for  life,  and  therefore 
cannot  be  attributed  to  the  agency  of  natural  selection. 
Now  this  fact  of  beauty  in  organic  structures  is  a  fact 
of  wide  generality — almost  as  wide,  indeed,  as  is  the 
fact  of  their  utility.  Mr.  Darwin,  therefore,  suggested 
another  hypothesis  whereby  to  render  a  scientific 
explanation  of  this  fact.  Just  as  by  his  theory  of 
natural  selection  he  sought  to  explain  the  major  fact 
of  utility,  so  did  he  endeavour  to  explain  the  minor 
fact  of  beauty  by  a  theory  of  what  he  termed  Sexual 
Selection. 


380          Darwin,  and  after  Darwin. 

It  is  a  matter  of  observation  that  the  higher 
animals  do  not  pair  indiscriminately ;  but  that  the 
members  of  either  sex  prefer  those  individuals  of  the 
opposite  sex  which  are  to  them  most  attractive.  It 
is  important  to  understand  in  limine  that  nobody  has 
ever  attempted  to  challenge  this  statement.  In  other 
words,  it  is  an  unquestionable  fact  that  among  many  of 
the  higher  animals  there  literally  and  habitually  occurs 
a  sexual  selection  ;  and  this  fact  is  not  a  matter  of 
inference,  but,  as  I  have  said,  a  matter  of  observation. 
The  inference  only  begins  where,  from  this  observable 
fact,  it  is  argued, — ist,  that  the  sexual  selection  has 
reference  to  an  aesthetic  taste  on  the  part  of  the 
animals  themselves  ;  and  2nd,  that,  supposing  the 
selection  to  be  determined  by  such  a  taste,  the  cause 
thus  given  is  adequate  to  explain  the  phenomena  of 
beauty  which  are  presented  by  these  animals.  I  will 
consider  these  two  points  separately. 

From  the  evidence  which  Darwin  has  collected,  it 
appears  to  me  impossible  to  doubt  that  an  aesthetic 
sense  is  displayed  by  many  birds,  and  not  a  few 
mammals.  This  of  course  does  not  necessarily  imply 
that  the  standards  of  such  a  sense  are  the  same  as 
our  own ;  nor  does  it  necessarily  imply  that  there  is 
any  constant  relation  between  such  a  sense  and  high 
levels  of  intelligence  in  other  respects.  In  point  of 
fact,  such  is  certainly  not  the  case,  because  the  best 
evidence  that  we  have  of  an  aesthetic  sense  in  animals 
is  derived  from  birds,  and  not  from  mammals.  The 
most  cogent  cases  to  quote  in  this  connexion  are 
those  of  the  numerous  species  of  birds  which  habi- 
tually adorn  their  nests  with  gaily  coloured  feathers, 
wool,  cotton,  or  any  other  gaudy  materials  which  they 


The   Theory  of  Sexual  Selection.       381 

may  find  lying  about  the  woods  and  fields.  In  many 
cases  a  marked  preference  is  shown  for  particular 
objects — as,  for  instance,  in  the  case  of  the  Syrian 
nut-hatch,  which  chooses  the  iridescent  wings  of 
insects,  or  that  of  the  great  crested  fly-catcher,  which 
similarly  chooses  the  cast-off  skins  of  snakes.  But 
no  doubt  the  most  remarkable  of  these  cases  is  that 
of  the  baya-bird  of  Asia,  which  after  having  com- 
pleted its  bottle-shaped  and  chambered  nest 1,  studs  it 
over  with  small  lumps  of  clay,  both  inside  and  out, 
upon  which  the  cock-bird  sticks  fire-flies,  apparently 
for  the  sole  purpose  of  securing  a  brilliantly  decorative 
effect.  Other  birds,  such  as  the  hammer-head  of 
Africa,  adorn  the  surroundings  of  their  nests  (which 
are  built  upon  the  ground)  with  shells,  bones,  pieces 
of  broken  glass  and  earthenware,  or  any  objects  of  a 
bright  and  conspicuous  character  which  they  may 
happen  to  find.  The  most  consummate  artists  in  this 
respect  are.  however,  the  bower-birds  ;  for  the  species 
of  this  family  construct  elaborate  play-houses  in  the 
form  of  arched  tunnels,  built  of  twigs  upon  the  ground. 
Through  and  around  such  a  tunnel  they  chase  one 
another  ;  and  it  is  always  observable  that  not  only  is 
the  floor  paved  with  a  great  collection  of  shells,  bones, 
coloured  stones,  and  any  other  brilliant  objects  which 
they  are  able  to  carry  in  their  beaks,  but  also  that  the 
walls  are  decorated  with  the  most  gaudy  articles 
which  the  birds  can  find.  There  is  one  genus,  in 
Papua,  which  even  goes  so  far  as  to  provide  the 
theatre  with  a  surrounding  garden.  A  level  piece  of 

1  The  chambers  are  three  in  number.  The  two  upper  ones  are 
occupied  respectively  by  the  male  and  the  sitting  female.  The  lower 
one  serves  as  a  general  living  room  when  the  young  are  hatched. 


382  Darwin,  and  after  Darwin. 

ground  is  selected  as  a  site  for  the  building.  The 
latter  is  about  two  feet  high,  and  constructed  round 
the  growing  stalk  of  a  shrub,  which  therefore  serves 
as  a  central  pillar  to  which  the  frame-work  of  the 
roof  is  attached.  Twigs  are  woven  into  this  frame- 
work until  the  whole  is  rendered  rain-proof.  The  tent 


FlG.  121. — The  Garden  Bower-bird  {Amblyortds  inornata  .     Reduced 
from  Gould's  Birds  of  New  Guinea  to  £  nat.  size. 

thus  erected  is  about  nine  feet  in  circumference  at  its 
base,  and  presents  a  large  arch  as  an  entrance.  The 
central  pillar  is  banked  up  with  moss  at  its  base,  and 
a  gallery  is  built  round  the  interior  of  the  edifice. 
This  gallery  is  decorated  with  flowers;  fruits;  fungi,  &c. 
These  are  also  spread  over  the  garden,  which  covers 


The   Theory  of  Sexual  Selection.       383 

about  the  same  area  as  the  play-house.  The  flowers 
are  said  to  be  removed  when  they  fade,  while  fresh 
ones  are  gathered  to  supply  their  places.  Thus  the 
garden  is  always  kept  bright  with  flowers,  as  well  as 
with  the  brilliant  green  of  mosses,  which  are  col- 
lected and  distributed  in  patches,  resembling  tiny 
lawns. 

Now  these  sundry  cases  alone  seem  to  prove  a  high 
degree  of  the  aesthetic  sense  as  occurring  among 
birds  ;  for,  it  is  needless  to  say,  none  of  the  facts  just 
mentioned  can  be  due  to  natural  selection,  seeing  that 
they  have  no  reference  to  utility,  or  the  preservation 
of  life.  But  if  an  aesthetic  sense  occurs  in  birds,  we 
should  expect,  on  a  priori  grounds,  that  it  would 
probably  be  exercised  with  refere'nce  to  the  personal 
appearance  of  the  sexes.  And  this  expectation  is 
fully  realized.  For  it  is  an  observable  fact  that  in 
most  species  of  birds  where  the  males  are  remarkable 
for  the  brilliancy  of  their  plumage,  not  only  is  this 
brilliancy  most  remarkable  during  the  pairing  season, 
but  at  this  season  also  the  male  birds  take  elaborate 
pains  to  display  their  charms  before  the  females. 
Then  it  is  that  the  peacock  erects  his  tail  to  strut 
round  and  round  the  hens,  taking  care  always  to 
present  to  them  a  front  view,  where  the  coloration  is 
most  gorgeous.  And  the  same  is  true  of  all  other 
gaily  coloured  male  birds.  During  the  pairing 
season  they  actively  compete  with  one  another  in 
exhibiting  their  attractiveness  to  the  females  ;  and  in 
many  cases  there  are  added  all  sorts  of  extraordinary 
antics  in  the  way  of  dancings  and  Growings.  Again, 
in  the  case  of  all  song-birds,  the  object  of  the  singing 
is  to  please  the  females ;  and  for  this  purpose  the 


384          Darwin,  and  after  Darwin. 

males  rival  one  another  to  the  best  of  their  musical 
ability. 

Thus  there  can  be  no  question  that  the  courtship 
of  birds  is  a  highly  elaborate  business,  in  which  the 
males  do  their  best  to  surpass  one  another  in  charming 
the  females.  Obviously  the  inference  is  that  the  males 
do  not  take  all  this  trouble  for  nothing  ;  but  that  the 
females  give  their  consent  to  pair  with  the  males 
whose  personal  appearance,  or  whose  voice,  proves  to 
be  the  most  attractive.  But,  if  so,  the  young  of  the 
male  bird  who  is  thus  selected  will  inherit  his  superior 
beauty ;  and  thus,  in  successive  generations,  a  con- 
tinuous advance  will  be  made  in  the  beauty  of 
plumage  or  of  song,  as  the  case  may  be, — both  the 
origin  and  development  of  beauty  in  the  animal  world 
being  thus  supposed  due  to  the  aesthetic  taste  of 
animals  themselves. 

Such  is  the  theory  of  sexual  selection  in  its  main 
outlines ;  and  with  regard  to  it  we  must  begin  by 
noting  two  things  which  are  of  most  importance.  In 
the  first  place,  it  is  a  theory  wholly  and  completely 
distinct  from  the  theory  of  natural  selection  ;  so  that 
any  truth  or  error  in  the  one  does  not  in  the  least 
affect  the  other.  The  second  point  is,  that  there  is 
not  so  great  a  wealth  of  evidence  in  favour  of  sexual 
selection  as  there  is  in  favour  of  natural  selection ; 
and,  therefore,  that  while  all  naturalists  nowadays 
accept  natural  selection  as  a  (whether  or  not  the]  cause 
of  adaptive,  useful,  or  life-preserving  structures,  there 
is  no  such  universal— but  only  a  very  general — agree- 
ment with  reference  to  sexual  selection  as  a  cause 
of  decorative,  beautiful,  or  life-embellishing  struc- 
tures. Nevertheless,  the  evidence  in  favour  of  sexual 


The  Theory  of  Sexual  Selection.       385 

selection   is  both   large  in  amount   and   massive  in 
weight. 

Our  consideration  of  this  evidence  will  bring  us  to 
the  second  division  of  our  subject,  as  previously  marked 
out  for  discussion — namely,  granting  that  an  aesthetic 
sense  occurs  in  certain  large  divisions  of  the  animal 
kingdom,  what  is  the  proof  that  such  a  sense  is  a 
cause  of  the  beauty  which  is  presented  by  the  animals 
in  question? 

Before  proceeding  to  state  this  proof,  however,  it 
is  desirable  to  observe  that  under  the  theory  of  sexual 
selection  Darwin  has  included  two  essentially  different 
classes  of  facts.  For  besides  the  large  class  of  facts 
to  which  I  have  thus  far  been  alluding, — i.  e.  the  cases 
where  two  sexes  of  the  same  species  differ  from  one 
another  in  respect  of  ornamentation, — there  is  another 
class  of  facts  equally  important,  namely,  the  cases 
where  the  two  sexes  of  the  same  species  differ  from 
one  another  in  respect  of  size,  strength,  and  the 
possession  of  natural  weapons,  such  as  spurs,  horns, 
&c.  In  most  of  these  cases  it  is  the  males  which 
are  thus  superiorly  endowed  ;  and  it  is  a  matter  of 
observation  that  in  all  cases  where  they  are  so  en- 
dowed they  use  their  superior  strength  and  natural 
weapons  for  fighting  together,  in  order  to  secure 
possession  of  the  females.  Hence  results  what  Mr. 
Darwin  has  called  the  Law  of  Battle  between  males 
of  the  same  species ;  and  this  law  of  battle  he  includes 
under  his  theory  of  sexual  selection.  But  it  is  evident 
that  the  principle  which -is  operative  in  the  law  of 
battle  differs  from  the  principle  which  is  concerned  in 
the  form  of  sexual  selection  that  has  to  do  with 
embellishment,  and  consequent  charm.  The  law  of 

*  C  c 


386          Darwin,  and  after  Darwin. 

battle,  in  fact,  more  nearly  approaches  the  law  of 
natural  selection  ;  seeing  that  it  expresses  the  natural 
advantages  of  brute  force  in  the  struggling  of  rival 
animals,  and  so  frequently  results  in  death  of  the  less 
fitted,  as  distinguished  from  a  mere  failure  to  propa- 
gate. Now  against  this  doctrine  of  the  law  of  battle, 
and  the  consequences  to  which  it  leads  in  the  superior 
fighting  powers  of  male  animals,  no  objection  has 
been  raised  in  any  quarter.  It  is  only  with  regard  to 
the  other  aspect  of  the  theory  of  sexual  selection— 
or  that  which  is  concerned  with  the  superior  em- 
bellishment of  male  animals — that  any  difference  of 
opinion  obtains.  I  will  now  proceed  to  give  the 
main  arguments  on  both  sides  of  this  question, 
beginning  with  a  resume  of  the  evidences  in  favour  of 
sexual  selection. 

In  the  first  place,  the  fact  that  secondary  sexual 
characters  of  the  embellishing  kind  are  so  generally 
restricted  to  the  male  sex  in  itself  seems  to  constitute 
very  cogent  proof  that,  in  some  way  or  another,  such 
characters  are  connected  with  the  part  which  is  played 
by  the  male  in  the  act  of  propagation.  Moreover, 
secondary  sexual  characters  of  this  kind  are  of  quite 
as  general  occurrence  as  are  those  of  the  other  kind 
which  have  to  do  with  rivalry  in  battle  ;  and  the  former 
are  usually  of  the  more  elaborate  description.  There- 
fore, as  there  is  no  doubt  that  secondary  sexual  char- 
acters of  the  one  order  have  an  immediate  purpose  to 
serve  in  the  act  of  propagation,  we  are  by  this  close 
analogy  confirmed  in  our  surmise  that  secondary  sexual 
characters  of  the  other,  and  still  more  elaborate,  order 
are  likewise  so  concerned.  Moreover,  this  view  of  their 
meaning  becomes  still  further  strengthened  when  we 


The   Theory  of  Sexual  Selection.       387 

take  into  consideration  the  following  facts.  Namely, 
(a)  secondary  sexual  characters  of  the  embellishing 
kind  are,  as  a  rule,  developed  only  at  maturity;  and 
most  frequently  during  only  a  part  of  the  year,  which 
is  invariably  the  breeding  season  :  (b)  they  are  always 
more  or  less  seriously  affected  by  emasculation:  (c) 
they  are  always,  and  only,  displayed  in  perfection 
during  the  act  of  courtship  :  (d]  then,  however,  they  are 
displayed  with  the  most  elaborate  pains  ;  yet  always, 
and  only,  before  the  females :  (e]  they  appear,  at  all 
events  in  many  cases,  to  have  the  effect  of  charming 
the  females  into  a  performance  of  the  sexual  act ; 
while  it  is  certain  that  in  many  cases,  both  among 
quadrupeds  and  birds,  individuals  of  the  one  sex  are 
capable  of  feeling  a  strong  antipathy  against,  or  a  strong 
preference  for,  certain  individuals  of  the  opposite  sex. 
Such  are  the  main  lines  of  evidence  in  favour  of  the 
theory  of  sexual  selection.  And  although  it  is  enough 
that  some  of  them  should  be  merely  stated  as  above 
in  order  that  their  immense  significance  should  be- 
come apparent,  in  the  case  of  others  a  bare  statement 
is  not  sufficient  for  this  purpose.  More  especially  is 
this  the  case  as  regards  the  enormous  profusion,  variety, 
and  elaboration  of  sexually- embellishing  characters 
which  occur  in  birds  and  mammals — not  to  mention 
several  divisions  of  Arthropoda  ;  together  with  the 
extraordinary  amount  of  trouble  which,  in  a  no  less 
extraordinary  number  of  different  ways,  is  taken  by 
the  male  animals  to  display  their  embellishments 
before  the  females.  And  even  in  many  cases  where 
to  our  eyes  there  is  no  particular  embellishment  to 
display,  the  process  of  courtship  consists  in  such  an 
elaborate  performance  of  dancings,  struttings,  and 
C  c  2 


388  Darwin,  and  ajter  Darwin. 

attitudinizings  that  it  is  scarcely  possible  to  doubt  their 
object  is  to  incite  the  opposite  sex.     Here,  for  instance, 


FIG.  122. — Courtship  of  Spiders.  A  few  examples  of  some  of  the 
attitudes  adopted  by  different  species  of  males  when  approaching  their 
females.  (After  Peckhain.) 

is  a  series   of  drawings  illustrating  the  courtship  of 
spiders.     I   choose  this  case   as  an  example,  partly 


The   Theory  of  Sexual  Selection.       389 


FIG.  r23- — Courtship  of  Spiders.  Continued  from  Fig.  122,  similaily 
showing  some  of  the  attitudes  of  approach  adopted  by  males  ol  yet 
other  different  species.  (After  Peckham.) 


3QO          Darwin,  and  after  Darwin. 

because  it  is  the  one  which  has  been  published  most 
recently,  and  partly  because  it  is  of  particular  interest 
as  occurring  so  low  down  in  the  zoological  scale.  I 
am  indebted  to  the  kindness  of  Mr.  and  Mrs.  Peckham 
for  permission  to  reproduce  these  few  selected  drawings 
from  their  very  admirable  work,  which  is  published  by 
the  Natural  History  Society  of  Wisconsin,  U.S.  It  is 
evident  at  a  glance  that  all  these  elaborate,  and  to  our 
eyes  ludicrous,  performances  are  more  suggestive  of 
incitation  than  of  any  other  imaginable  purpose.  And 
this  view  of  the  matter  is  strongly  corroborated  by 
the  fact  that  it  is  the  most  brightly  coloured  parts  of 
the  male  spiders  which  are  most  obtruded  upon  the 
notice  of  the  female  by  these  peculiar  attitudes — in 
just  the  same  way  as  is  invariably  the  case  in  the 
analogous  phenomena  of  courtship  among  birds, 
insects,  &c. 

But  so  great  is  the  mass  of  material  which  Darwin 
-has  collected  in  proof  of  all  the  points  mentioned  in 
the  foregoing  paragraph,  that  to  attempt  anything 
in  the  way  of  an  epitome  would  really  be  to  damage 
its  evidential  force.  Therefore  I  deem  it  best  simply 
to  refer  to  it  as  it  stands  in  his  Descent  of  Man, 
concluding,  as  he  concludes, — "  This  surprising  uni- 
formity in  the  laws  regulating  the  differences  between 
the  sexes  in  so  many  and  such  widely  separated 
classes  is  intelligible  if  we  admit  the  action  throughout 
all  the  higher  divisions  of  the  animal  kingdom  of  one 
common  cause,  namely,  sexual  selection  "  ;  while,  as 
he  might  well  have  added,  it  is  difficult  to  imagine 
that  all  the  large  classes  of  facts  which  an  admission  of 
this  common  cause  serves  to  explain,  can  ever  admit 
of  being  rendered  intelligible  by  yny  other  theory. 


The   Theory  of  Sexual  Selection.       391 

We  may  next  proceed  to  consider  the  objections 
which  have  been  brought  against  the  theory  of  sexual 
selection.  And  this  is  virtually  the  same  thing  as 
saying  that  we  may  now  consider  Mr.  Wallace's  views 
upon  the  subject 

Reserving  for  subsequent  consideration  the  most 
general  of  these  objections— namely,  that  at  best  the 
theory  can  only  apply  to  the  more  intelligent  animals, 
and  so  must  necessarily  fail  to  explain  the  phenomena 
of  beauty  in  the  less  intelligent,  or  in  the  non- 
intelligent,  as  well  as  in  all  species  of  plants — we  may 
take  seriatim  the  other  objections  which,  in  the  opinion 
of  Mr.  Wallace,  are  sufficient  to  dispose  of  the  theory 
even  as  regards  the  higher  animals. 

In  the  first  place,  he  argues  that  the  principal 
cause  of  the  greater  brilliancy  of  male  animals  in 
general,  and  of  male  birds  in  particular,  is  that  they 
do  not  so  much  stand  in  need  of  protection  arising 
from  concealment  as  is  the  case  with  their  respective 
females.  Consequently  natural  selection  is  not  so 
active  in  repressing  brilliancy  of  colour  in  the  males, 
or,  which  amounts  to  the  same  thing,  is  more  active 
in  "  repressing  in  the  female  those  bright  colours 
which  are  normally  produced  in  both  sexes  by  general 
laws." 

Next,  he  argues  that  not  only  does  natural  selection 
thus  exercise  a  negative  influence  in  passively  per- 
mitting more  heightened  colour  to  appear  in  the 
males,  but  even  exercises  a  positive  influence  in 
actively  promoting  its  development  in  the  males, 
while,  at  the  same  time,  actively  repressing  its  ap- 
pearance in  the  females.  For  heightened  colour,  he 
says,  is  correlated  with  health  and  vigour  ;  and  as  there 


392          Darwin,  and  after  Darwin. 

can  be  no  doubt  that  healthy  and  vigorous  birds  best 
provide  for  their  young,  natural  selection,  by  always 
placing  its  premium  on  health  and  vigour  in  the  males, 
thus  also  incidentally  promotes,  through  correlated 
growth,  their  superior  coloration. 

Again,  with  regard  to  the  display  which  is  practised 
by  male  birds,  and  which  constitutes  the  strongest 
of  all  Mr.  Darwin's  arguments  in  favour  of  sexual 
selection,  Mr.  Wallace  points  out  that  there  is  no 
evidence  of  the  females  being  in  any  way  affected 
thereby.  On  the  other  hand,  he  argues  that  this 
display  may  be  due  merely  to  general  excitement ; 
and  he  lays  stress  upon  the  more  special  fact  that 
moveable  feathers  are  habitually  erected  under  the 
influence  of  anger  and  rivalry,  in  order  to  make  the 
bird  look  more  formidable  in  the  eyes  of  antago- 
nists. 

Furthermore,  he  adduces  the  consideration  that, 
even  if  the  females  are  in  any  way  affected  by  colour 
and  its  display  on  the  part  of  the  males,  and  if,  there- 
fore, sexual  selection  be  conceded  a  true  principle  in 
theory,  still  we  must  remember  that,  as  a  matter  of 
fact,  it  can  only  operate  in  so  far  as  it  is  allowed  to 
operate  by  natural  selection.  Now,  according  to  Mr. 
Wallace,  natural  selection  must  wholly  neutralize  any 
such  supposed  influence  of  sexual  selection.  For, 
unless  the  survivors  in  the  general  struggle  for  exis- 
tence happen  to  be  those  which  are  also  the  most 
highly  ornamented,  natural  selection  must  neutralize 
and  destroy  any  influence  that  may  be  exerted  by 
female  selection.  But  obviously  the  chances  against 
the  otherwise  best  fitted  males  happening  to  be  like- 
wise the  most  highly  ornamented  must  be  many  to 


The  Theory  of  Sexual  Selection.       393 

one,  unless,  as  Wallace  supposes,  there  is  some  cor- 
relation between  embellishment  and  general  perfection, 
in  which  case,  as  he  points  out,  the  theory  of  sexual 
selection  lapses  altogether,  and  becomes  but  a  special 
case  of  natural  selection. 

Once  more,  Mr.  Wallace  argues  that  the  evidence 
collected  by  Mr.  Darwin  himself  proves  that  each  bird 
finds  a  mate  under  any  circumstances— a  general  fact 
which  in  itself  must  quite  neutralize  any  effect  of 
sexual  selection  of  colour  or  ornament,  since  the  less 
highly  coloured  birds  would  be  at  no  disadvantage  as 
regards  the  leaving  of  healthy  progeny. 

Lastly,  he  urges  the  high  improbability  that  through 
thousands  of  generations  all  the  females  of  any  par- 
ticular species — possibly  spread  over  an  enormous 
area — should  uniformly  and  always  have  displayed 
exactly  the  same  taste  with  respect  to  every  detail  of 
colour  to  be  presented  by  the  males. 

Now,  without  any  question,  we  have  here  a  most 
powerful  array  of  objections  against  the  theory  of 
sexual  selection.  Each  of  them  is  ably  developed  by 
Mr.  Wallace  himself  in  his  work  on  Tropical  Nature ; 
and  although  I  have  here  space  only  to  state  them  in 
the  most  abbreviated  of  possible  forms,  I  think  it  will 
be  apparent  how  formidable  these  objections  appear. 
Unfortunately  the  work  in  which  they  are  mainly  pre- 
sented was  published  several  years  after  the  second 
edition  of  the  Descent  of  Man,  so  that  Mr.  Darwin 
never  had  a  suitable  opportunity  of  replying.  But,  if 
he  had  had  such  an  opportunity,  as  far  as  I  can  judge 
it  seems  that  his  reply  would  have  been  more  or  less 
as  follows. 

In  the  first  place,  Mr.  Wallace  fails  to  distinguish 


394  Darwin,  and  after  Darwin. 

between  brilliancy  and  ornamentation — or  between 
colour  as  merely  '  heightened,"  and  as  distinctively 
decorative.  Yet  there  is  obviously  the  greatest  pos- 
sible difference  between  these  two  things.  We  may 
readily  enough  admit  that  a  mere  heightening  of  al- 
ready existing  coloration  is  likely  enough — at  all 
events  in  many  cases — to  accompany  a  general  increase 
of  vigour,  and  therefore  that  natural  selection,  by  pro- 
moting the  latter,  may  also  incidentally  promote  the 
former,  in  cases  where  brilliancy  is  not  a  source  of 
danger.  But  clearly  this  is  a  widely  different  thing  from 
showing  that  not  only  a  general  brilliancy  of  colour, 
but  also  the  particular  disposition  of  colours^  in  the 
form  of  ornamental  patterns,  can  thus  be  accounted 
for  by  natural  selection.  Indeed,  it  is  expressly  in 
order  to  account  for  the  occurrence  of  such  ornamental 
patterns  that  .Mr.  Darwin  constructed  his  theory  of 
sexual  selection ;  and  therefore,  by  thus  virtually 
ignoring  the  only  facts  which  that  theory  endeavours 
to  explain,  Mr.  Wallace  is  not  really  criticizing  the 
theory  at  all.  By  representing  that  the  theory  has  to 
do  only  with  brilliancy  of  colour,  as  distinguished 
from  disposition  of  colours,  he  is  going  off  upon  a 
false  issue  which  has  never  really  been  raised  \  Look, 
for  example,  at  a  peacock's  tail.  No  doubt  it  is  suf- 
ficiently brilliant  ;  but  far  more  remarkable  than  its 
brilliancy  is  its  elaborate  pattern  on  the  one  hand,  and 
its  enormous  size  on  the  other.  There  is  no  conceiv- 
able reason  why  mere  brilliancy  of  colour,  as  an  ac- 
cidental concomitant  of  general  vigour,  should  have 
run  into  so  extraordinary,  so  elaborate,  and  so  bcau- 

1  Note  C. 


The   Theory  of  Sexual  Selection.       395 

tiful  a  design  of  colours.  Moreover,  this  design  is  only 
unfolded  when  the  tail  is  erected,  and  the  tail  is  not 
erected  in  battle  (as  Mr.  Wallace's  theory  of  the 
erectile  function  in  feathers  would  require),  but  in 
courtship  ;  obviously,  therefore,  the  purpose  of  the 
pattern,  so  to  speak,  is  correlated  with  the  act  of 
courtship— it  being  only  then,  in  fact,  that  the  general 
purpose  of  the  whole  structure,  as  well  as  the  more 
special  purpose  of  the  pattern,  becomes  revealed. 
Lastly,  the  fact  of  this  whole  structure  being  so  large, 
entailing  not  only  a  great  amount  of  physiological 
material  in  its  production,  but  also  of  physiological 
energy  in  carrying  about  such  a  weight,  as  well  as  of 
increased  danger  from  impeding  locomotion  and  in- 
viting capture — all  this  is  obviously  incompatible  with 
the  supposition  of  the  peacock's  tail  having  been  pro- 
duced by  natural  selection.  And  such  a  case  does 
not  stand  alone.  There  are  multitudes  of  other  in- 
stances of  ornamental  structures  imposing  a  drain 
upon  the  vital  energies  of  their  possessors,  without 
conferring  any  compensating  benefit  from  a  utilitarian 
point  of  view.  Now,  in  all  these  cases,  without  any 
exception,  such  structures  are  ornamental  structures 
which  present  a  plain  and  obvious  reference  to  the 
relationship  of  the  sexes.  Therefore  it  becomes  almost 
impossible  to  doubt — first,  that  they  exist  for  the  sake 
of  ornament ;  and  next,  that  the  ornament  exists  on 
account  of  that  relationship.  If  such  structures  were 
due  merely  to  a  superabundance  of  energy,  as  Mr. 
Wallace  supposes,  not  only  ought  they  to  have  been 
kept  down  by  the  economizing  influence  of  natural 
selection  ;  but  we  can  see  no  reason,  either  why  they 
should  be  so  highly  ornamental  on  the  one  hand,  or 


396          Darwin,  and  after  Darwin. 

so  exclusively  related  to  the  sexual  relationship  on  the 
other. 

Finally,  we  must  take  notice  of  the  fact  that  where 
peculiar  structures  are  concerned  for  purposes  of  dis- 
play in  courtship,  the  elaboration  of  these  structures  is 
often  no  less  remarkable  than  that  of  patterns  where 


I'lG.  124 — The  Bell-bird  (Chasmorhynchus  nivens,  £  natural  size). 
Drawn  from  nature  {R.  Coll.  Surg.  Mus.}.  In  the  drawing  of  the 
adult  male  the  ornamental  appendage  is  represented  in  its  inflated 
condition,  during  courtship ;  in  the  drawing  of  the  young  male  it  is 
shown  in  its  flaccid  condition. 

colours  are  thus  concerned.  Take,  for  example,  the  case 
of  the  Bell-bird,  which  I  select  from  an  innumerable 
number  of  instances  that  might  be  mentioned  because, 
while  giving  a  verbal  description  of  this  animal, 
Darwin  does  not  supply  a  pictorial  representation 


The   Theory  of  Sexual  Selection.       397 

thereof.  The  bird,  which  lives  in  South  America,  has 
a  very  loud  and  peculiar  call,  that  can  be  heard  at  a 
distance  of  two  or  three  miles.  The  female  is  dusky- 
green  ;  but  the  adult  male  is  a  beautiful  white,  ex- 
cepting the  extraordinary  structure  with  which  we 
are  at  present  concerned.  This  is  a  tube  about  three 


FIG.  ii^.—C.tricarunculatus,  \  natural  size.  Copied  from  the  Ibis. 
The  ornamental  appendages  of  the  male  are  represented  in  a  partly 
inflated  condition. 

inches  long,  which  rises  from  the  base  of  the  beak. 
It  is  jet  black,  and  dotted  over  with  small  downy 
feathers.  The  tube  is  closed  at  the  top,  but  its  cavity 
communicates  with  the  palate,  and  thus  the  whole 
admits  of  being  inflated  from  within,  when,  of  course, 
it  stands  erect  as  represented  in  one  of  the  two  draw- 


398  Danvin,  and  after  Darwin. 

ings.  When  not  thus  inflated,  it  hangs  down,  as 
shown  in  the  second  figure,  which  represents  the 
plumage  of  a  young  male.  (Fig.  124.) 

In  another  species  of  the  genus  there  are  three  of  these 
appendages — the  two  additional  ones  being  mounted 
on  the  corners  of  the  mouth.  (Fig.  125.)  In  all  species 
of  the  genus  (four  in  number)  the  tubes  are  inflated 
during  courtship,  and  therefore  perform  the  function 
of  sexual  embellishments.  Now  the  point  to  which  I 
wish  to  draw  attention  is,  that  so  specialized  and  mor- 
phologically elaborate  a  structure  cannot  be  regarded 
as  merely  adventitious.  It  must  have  been  developed 
by  some  definite  cause,  acting  through  a  long  series  of 
generations.  And  as  no  other  function  can  be  as- 
signed to  it  than  that  of  charming  the  female  when  it 
is  erected  in  courtship,  the  peculiarity  of  form  and 
mechanism  which  it  presents — like  the  elaboration  of 
patterns  in  cases  where  colour  only  is  concerned — 
virtually  compels  us  to  recognise  in  sexual  selection 
the  only  conceivable  cause  of  its  production. 

For  these  reasons  I  think  that  Mr.  Wallace's  main 
objection  falls  to  the  ground.  Passing  on  to  his  sub- 
sidiary objections,  I  do  not  see  much  weight  in  his 
merely  negative  difficulty  as  to  there  being  an  absence 
of  evidence  upon  hen  birds  being  charmed  by  the 
plumage,  or  the  voice,  of  their  consorts.  For,  on  the 
one  hand,  it  is  not  very  safe  to  infer  what  sentiments 
may  be  in  the  mind  of  a  hen  ;  and,  on  the  other  hand, 
it  is  impossible  to  conceive  what  motive  can  be  in  the 
mind  of  a  cock,  other  than  that  of  making  himself 
attractive,  when  he  performs  his  various  antics,  displays 
his  ornamental  plumes,  or  sings  his  melodious  songs. 
Considerations  somewhat  analogous  apply  to  the 


The   Theory  of  Sexual  Selection.       399 

difficulty  of  supposing  so  much  similarity  and  con- 
stancy of  taste  on  the  part  of  female  animals  as  Mr. 
Darwin's  theory  undoubtedly  requires.  Although  we 
know  very  little  about  the  psychology  of  the  lower 
animals,  we  do  observe  in  many  cases  that  small 
details  of  mental  organization  are  often  wonderfully 
constant  and  uniform  throughout  all  members  of  a 
species,  even  where  it  is  impossible  to  suggest  any 
utility  as  a  cause. 

Again,  as  regards  the  objection  that  each  bird  finds 
a  mate  under  any  circumstances,  we  have  here  an 
obvious  begging  of  the  whole  question.  That  every 
feathered  Jack  should  find  a  feathered  Jill  is  perhaps 
what  we  might  have  antecedently  expected  ;  but  when 
we  meet  with  innumerable  instances  of  ornamental 
plumes,  melodious  songs,  and  the  rest,  as  so  many 
witnesses  to  a  process  of  sexual  selection  having 
always  been  in  operation,  it  becomes  irrational  to  ex- 
clude such  evidence  on  account  of  our  antecedent 
prepossessions. 

There  remains  the  objection  that  the  principles  of 
natural  selection  must  necessarily  swallow  up  those  of 
sexual  selection.  And  this  consideration,  I  doubt 
not,  lies  at  the  root  of  all  Mr.  Wallace's  opposition  to 
the  supplementary  theory  of  sexual  selection.  He  is 
self-consistent  in  refusing  to  entertain  the  evidence  of 
sexual  selection,  on  the  ground  of  his  antecedent  per- 
suasion that  in  the  great  drama  of  evolution  there  is 
no  possible  standing-ground  for  any  other  actor  than 
that  which  appears  in  the  person  of  natural  selection. 
But  here,  again,  we  must  refuse  to  allow  any  merely 
antecedent  presumption  to  blind  our  eyes  to  the 
actual  evidence  of  other  agencies  having  co-operated 


400          Darwin,  and  after  Darwin. 

with  natural  selection  in  producing  the  observed  results. 
And,  as  regards  the  particular  case  now  before  us,  I 
think  I  have  shown,  as  far  as  space  will  permit,  that 
in  the  phenomena  of  decorative  colouring  (as  distin- 
guished from  merely  brilliant  colouring),  of  melodious 
song  (as  distinguished  from  merely  tuneless  cries),  of 
enormous  arborescent  antlers  (as  distinguished  from 
merely  offensive  weapons),  and  so  forth — I  say  that  in 
all  these  phenomena  we  have  phenomena  which  can- 
not possibly  be  explained  by  the  theory  of  natural 
selection  ;  and,  further,  that  if  they  are  to  be  explained 
at  all,  this  can  only  be  done,  so  far  as  we  can  at 
present  see.  by  Mr.  Darwin's  supplementary  theory  of 
sexual  selection. 

I  have  now  briefly  answered  all  Mr.  Wallace's 
objections  to  this  supplementary  theory,  and,  as  pre- 
viously remarked,  I  feel  pretty  confident  that,  at  all 
events  in  the  main,  the  answer  is  such  as  Mr.  Darwin 
would  himself  have  supplied,  had  there  been  a  third 
edition  of  his  work  upon  the  subject.  At  all  events, 
be  this  as  it  may,  we  are  happily  in  possession  of  un- 
questionable evidence  that  he  believed  all  Mr.  Wallace's 
objections  to  admit  of  fully  satisfactory  answers.  For 
his  very  last  words  to  science — read  only  a  few  hours 
before  his  death  at  a  meeting  of  the  Zoological 
Society — were : 

I  may  perhaps  be  here  permitted  to  say  that,  after  having 
carefully  weighed,  to  the  best  of  my  ability,  the  various  argu- 
ments which  have  been  advanced  against  the  principle  of  sexual 
selection,  I  remain  firmly  convinced  of  its  truth  '. 

1  Since  the  above  exposition  of  the  theory  of  sexual  selection  was 
written,  Mr.  Poulton  has  published  his  work  on  the  Colours  of  Animals. 
He  there  reproduces  some  of  the  illustrations  which  occur  in  Mr.  and 


The   Theory  of  Sexual  Selection.      401 

Concluding  Remarks. 

I  will  now  conclude  this  chapter,  and  with  it  the 
present  volume,  by  offering  a  few  general  remarks  on 
what  may  be  termed  the  philosophical  relations  of 
Darwinian  doctrine  to  the  facts  of  adaptation  on  the 
one  hand,  and  to  those  of  beauty  on  the  other.  Of 
course  we  are  all  aware  that  before  the  days  of  this 
doctrine  the  facts  of  adaptation  in  organic  nature  were 
taken  to  constitute  the  clearest  possible  evidence  of 
special  design,  on  account  of  the  wonderful  mechanisms 
which  they  everywhere  displayed  ;  while  the  facts  of 
beauty  were  taken  as  constituting  no  less  conclusive 
evidence  of  the  quality  of  such  special  design  as 
beneficent,  not  to  say  artistic.  But  now  that  the 
Darwinian  doctrine  appears  to  have  explained 
scientifically  the  former  class  of  facts  by  its  theory  of 
natural  selection,  and  the  latter  class  of  facts  by  its 
theory  of  sexual  selection,  we  may  fitly  conclude  this 
brief  exposition  of  the  doctrine  as  a  whole  by  consi- 
dering what  influence  such  naturalistic  explanations 
may  fairly  be  taken  to  exercise  upon  the  older,  or 
super-naturalistic,  interpretations. 

To  begin  with  the  facts  of  adaptation,  we  must 
first  of  all  observe  that  the  Darwinian  doctrine  is 
immediately  concerned  with  these  facts  only  in  so  far 

Mrs.  Peckham's  work  on  Sexual  Selection  in  Spiders,  and  furnishes 
appropriate  descriptions.  Therefore,  while  retaining  the  illustrations, 
I  have  withdrawn  my  own  descriptions. 

Mr.  Poulton  has  also  in  his  book  supplied  a  rlsumf  of  the  arguments 
for  and  against  the  theory  of  sexual  selection  in  general.  Of  course  in 
nearly  all  respects  this  corresponds  with  the  resume  which  is  given  in 
the  foregoing  pages;  but  I  have  left  the  latter  as  it  was  originally 
written,  because  all  the  critical  part  is  reproduced  verbatim  from  a 
review  of  Mr.  Wallace's  Darwinism,  of  a  date  still  earlier  than  that  of 
Mr.  Poulton's  book — viz.  Contemporary  Review,  August,  1889. 

*  D   d 


4O2  Darwin,  and  after  Darwin. 

as  they  occur  in  organic  nature.  With  the  adapta- 
tions— if  they  can  properly  be  so  called — which  occur 
in  all  the  rest  of  nature,  and  which  go  to  constitute  the 
Cosmos  as  a  whole  so  wondrous  a  spectacle  of 
universal  law  and  perfect  order,  this  doctrine  is  but 
indirectly  concerned.  Nevertheless,  it  is  of  course 
fundamentally  concerned  with  them  to  the  extent  that 
it  seeks  to  bring  the  phenomena  of  organic  nature  into 
line  with  those  of  inorganic  ;  and  therefore  to  show 
that  whatever  view  we  may  severally  take  as  to  the 
kind  of  causation  which  is  energizing  in  the  latter  we 
must  now  extend  to  the  former.  This  is  usually 
expressed  by  saying  that  the  theory  of  evolution  by 
natural  selection  is  a  mechanical  theory.  It  endea- 
vours to  comprise  all  the  facts  of  adaptation  in  organic 
nature  under  the  same  category  of  explanation  as 
those  which  occur  in  inorganic  nature — that  is  to 
say,  under  the  category  of  physical,  or  ascertainable, 
causation.  Indeed,  unless  the  theory  has  succeeded 
in  doing  this,  it  has  not  succeeded  in  doing  anything — 
beyond  making  a  great  noise  in  the  world.  If  Mr. 
Darwin  has  not  discovered  a  new  mechanical  cause  in 
the  selection  principle,  his  labour  has  been  worse  than 
in  vain. 

Now,  without  unduly  repeating  what  has  already 
been  said  in  Chapter  VIII,  I  may  remark  that,  what- 
ever we  may  each  think  of  the  measure  of  success 
which  has  thus  far  attended  the  theory  of  natural 
selection  in  explaining  the  facts  of  adaptation,  we  ought 
all  to  agree  that,  considered  as  a  matter  of  general 
reasoning,  the  theory  does  certainly  refer  to  a  vera 
causa  of  a  strictly  physical  kind  ;  and,  therefore,  that 
no  exception  can  be  taken  to  the  theory  in  this  respect 


The  Theory  of  Sexual  Selection.       403 

on  grounds  of  logic.  If  the  theory  in  this  respect  is  to 
be  attacked  at  all,  it  can  only  be  on  grounds  of  fact — 
namely,  by  arguing  that  the  cause  does  not  occur  in 
nature,  or  that,  if  it  does,  its  importance  has  been  exag- 
gerated by  the  theory.  Even,  however,  if  the  latter 
proposition  should  ever  be  proved,  we  may  now  be 
virtually  certain  that  the  only  result  would  be  the  rele- 
gation of  all  the  residual  phenomena  of  adaptation  to 
other  causes  of  the  physical  order — whether  known  or 
unknown.  Hence,  as  far  as  the  matter  of  principle  is 
concerned,  we  may  definitely  conclude  that  the  great 
naturalistic  movement  of  our  century  has  already 
brought  all  the  phenomena  of  adaptation  in  organic 
nature  under  precisely  the  same  category  of  mecha- 
nical causation,  as  similar  movements  in  previous 
centuries  have  brought  all  the  known  phenomena  of 
inorganic  nature :  the  only  question  that  remains  for 
solution  is  the  strictly  scientific  question  touching  the 
particular  causes  of  the  mechanical  order  which  have 
been  at  work. 

So  much,  then,  for  the  phenomena  of  adaptation. 
Turning  next  to  those  of  beauty,  we  have  already  seen 
that  the  theory  of  sexual  selection  stands  to  these  in 
precisely  the  same  relation  as  the  theory  of  natural 
selection  does  to  those  of  adaptation.  In  other  words, 
it  supplies  a  physical  explanation  of  them  ;  because, 
as  far  as  our  present  purposes  are  concerned,  it  may 
be  taken  for  granted,  or  for  the  sake  of  argument,  that 
inasmuch  as  psychological  elements  enter  into  the 
question  the  cerebral  basis  which  they  demand  involves 
a  physical  side. 

There  is,  moreover,  this  further  point  of  resemblance 
between  the  two  theories :  neither  of  them  has  any 
D  d  2 


404          Darwin,  and  after  Darwin. 

reference  to  inorganic  nature.  Therefore,  with  the 
charm  or  the  loveliness  of  landscapes,  of  earth  and  sea 
and  sky,  of  pebbles,  crystals,  and  so  forth,  we  have  at 
present  nothing  to  do.  How  it  is  that  so  many  inani- 
mate objects  are  invested  with  beauty—  why  it  is  that 
beauty  attaches  to  architecture,  music,  poetry,  and 
many  other  things  — these  are  questions  which  do  not 
specially  concern  the  biologist.  If  they  are  ever  to 
receive  any  satisfactory  explanation  in  terms  of 
natural  causation,  this  must  be  furnished  at  the  hands 
of  the  psychologist.  It  may  be  possible  for  him  to 
show,  more  satisfactorily  than  hitherto,  that  all  beauty, 
whenever  and  wherever  it  occurs,  is  literally  "  in  the 
eyes  of  the  beholder  " ;  or  that  objectively  considered, 
there  is  no  such  thing  as  beauty.  It  may  be — and  in 
my  opinion  it  probably  is — purely  an  affair  of  the 
percipient  mind  itself,  depending  on  the  association  of 
ideas  with  pleasure-giving  objects.  This  association 
may  well  lead  to  a  liking  for  such  objects,  and  so  to  the 
formation  of  what  is  known  as  aesthetic  feeling  with 
regard  to  them.  Moreover,  beauty  of  inanimate  nature 
must  be  an  affair  of  the  percipient  mind  itself,  unless 
there  be  a  creating  intelligence  with  organs  of  sense 
and  ideals  of  beauty  similar  to  our  own.  And,  apart 
from  any  deeper  considerations,  this  latter  possibility  is 
scarcely  entitled  to  be  regarded  as  a  probability,  looking 
to  the  immense  diversities  in  those  ideals  among  dif- 
ferent races  of  mankind.  But,  be  this  as  it  may,  the 
scientific  problem  which  is  presented  by  the  fact  of 
aesthetic  feeling,  even  if  it  is  ever  to  be  satisfactorily 
solved,  is  a  problem  which,  as  already  remarked,  must 
be  dealt  with  by  psychologists.  As  biologists  we  have 
simply  to  accept  this  feeling  as  a  fact,  and  to  consider 


The   Theory  of  Sexual  Selection.      405 

how,  out  of  such  a  feeling  as  a  cause,  the  beauty  of 
organic  nature  may  have  followed  as  an  effect. 

Now  we  have  already  seen  how  the  theory  of  sexual 
selection  supposes  this  to  have  happened.  But 
against  this  theory  a  formidable  objection  arises,  and 
one  which  I  have  thought  it  best  to  reserve  for  treat- 
ment in  this  place,  because  it  serves  to  show  the 
principal  difference  between  Mr.  Darwin's  two  great 
generalizations,  considered  as  generalizations  in  the 
way  of  mechanical  theory.  For  while  the  theory  of 
natural  selection  extends  equally  throughout  the  whole 
range  of  organic  nature,  the  theory  of  sexual  selection 
has  but  a  comparatively  restricted  scope,  which,  more- 
over, is  but  vaguely  defined.  For  it  is  obvious  that 
the  theory  can  only  apply  to  living  organisms  which 
are  sufficiently  intelligent  to  admit  of  our  reasonably 
accrediting  them  with  aesthetic  taste — namely,  in 
effect,  the  higher  animals.  And  just  as  this  con- 
sideration greatly  restricts  the  possible  scope  of  the 
theory,  as  compared  with  that  of  natural  selection,  so 
does  it  render  undefined  the  zoological  limits  within 
which  it  can  be  reasonably  employed.  Lastly,  this 
necessarily  undefined,  and  yet  most  important  limita- 
tion exposes  the  theory  to  the  objection  just  alluded 
to,  and  which  I  shall  now  mention. 

The  theory,  as  we  have  just  seen,  is  necessarily 
restricted  in  its  application  to  the  higher  animals. 
Yet  the  facts  which  it  is  designed  to  explain  are  not 
thus  restricted.  For  beauty  is  by  no  means  restricted 
to  the  higher  animals.  The  whole  of  the  vegetable 
world,  and  the  whole  of  the  animal  world  at  least  as 
high  up  in  the  scale  as  the  insects,  must  be  taken  as 
incapable  of  aesthetic  feeling.  Therefore,  the  extreme 


406          Darwin,  and  after  Darwin. 

beauty  of  flowers,  sea-anemones,  corab,  and  so  forth, 
cannot  possibly  be  ascribed  to  sexual  selection. 

Now,  with  regard  to  this  difficulty,  we  must  begin 
by  excluding  the  case  of  the  vegetable  kingdom  as 
irrelevant.  For  it  has  been  rendered  highly  probable — 
if  not  actually  proved — by  Darwin  and  others,  that  the 
beauty  of  flowers  and  of  fruits  is  in  large  part  due  to 
natural  selection.  It  is  to  the  advantage  of  flowering 
plants  that  their  organs  of  fructification  should  be 
rendered  conspicuous  —  and  in  many  cases  also 
odoriferous, — in  order  to  attract  the  insects  on  which 
the  process  of  fertilization  depends.  Similarly,  it  is 
to  the  advantage  of  all  plants  which  have  brightly 
coloured  fruits  that  these  should  be  conspicuous  for 
the  purpose  of  attracting  birds,  which  eat  the  fruits  and 
so  disseminate  the  seed.  Hence  all  the  gay  colours 
and  varied  forms,  both  of  flowers  and  fruits:  have  been 
thus  adequately  explained  as  due  to  natural  causes, 
working  for  the  welfare,  as  distinguished  from  the 
beauty,  of  the  plants.  For  even  the  distribution  of 
colours  on  flowers,  or  the  beautiful  patterns  which  so 
many  of  them  present,  are  found  to  be  useful  in  guiding 
insects  to  the  organs  of  fructification. 

Again,  the  green  colouring  of  leaves,  which  lends 
so  much  beauty  to  the  vegetable  world,  has  likewise 
been  shown  to  be  of  vital  importance  to  the  physiology 
of  plant-life ;  and,  therefore,  may  also  be  ascribed  to 
natural  selection.  Thus,  there  remains  only  the  forms 
of  plants  other  than  the  flowers.  But  the  forms  of 
leaves  have  also  in  many  cases  been  shown  to  be 
governed  by  principles  of  utility ;  and  the  same  is  to 
be  said  of  the  branching  structure  which  is  so 
characteristic  of  trees  and  shrubs,  since  this  is  the 


The  Theory  of  Sexual  Selection.      407 

form  most  effectual  for  spreading  out  the  leaves  to  the 
light  and  air.  Here,  then,  we  likewise  find  that  the 
cause  determining  plant  beauty  is  natural  selection ; 
and  so  we  may  conclude  that  the  only  reason  why 
the  forms  of  trees  which  are  thus  determined  by 
utility  appeal  to  us  as  beautiful,  is  because  we  are 
accustomed  to  these  the  most  ordinary  forms.  Our 
ideas  having  been  always,  as  it  were,  moulded  upon 
these  forms,  aesthetic  feeling  becomes  attached  to 
them  by  the  principle  of  association.  At  any  rate,  it 
is  certain  that  when  we  contemplate  almost  any  forms 
of  plant-structure  which,  for  special  reasons  of  utility, 
differ  widely  from  these  (to  us)  more  habitual  forms, 
the  result  is  not  suggestive  of  beauty.  Many  of  the 
tropical  and  un-tree-like  plants — such  as  the  cactus 
tribe — strike  us  as  odd  and  quaint,  not  as  beautiful. 
Be  this  however  as  it  may,  I  trust  I  have  said  enough 
to  prove  that  in  the  vegetable  world,  at  all  events,  the 
attainment  of  beauty  cannot  be  held  to  have  been  an 
object  aimed  at,  so  to  speak,  for  its  own  sake.  Even 
if,  for  the  purposes  of  argument,  we  were  to  suppose 
that  all  the  forms  and  colours  in  the  vegetable  world 
are  due  to  special  design,  there  could  be  no  doubt 
that  the  purpose  of  this  design  has  been  in  chief  part 
a  utilitarian  purpose  ;  it  has  not  aimed  at  beauty  ex- 
clusively for  its  own  sake.  For  most  of  such  beauty  as 
we  here  perceive  is  plainly  due  to  the  means  adopted 
for  the  attainment  of  life-preserving  ends,  which,  of 
course,  is  a  metaphorical  way  of  saying  that  it  is 
probably  due  to  natural  selection1. 

1  The  beauty  of  autumnal  tints  in  fading  leaves  may  possibly  be 
adduced  per  contra.  But  here  we  have  to  remember  that  it  is  only 
some  kinds  of  leaves  which  thus  become  beautiful  when  fading,  while, 


408          Darwin,  and  after  Darwin. 

Turning,  then,  to  the  animal  kingdom  below  the 
level  of  insects,  here  we  are  bound  to  confess  that 
the  beauty  which  so  often  meets  us  cannot  reasonably 
be  ascribed  either  to  natural  or  to  sexual  selection. 
Not  to  sexual  selection  for  the  reasons  already  given  ; 
the  animals  in  question  are  neither  sufficiently  in- 
telligent to  possess  any  aesthetic  taste,  nor,  as  a  matter 
of  fact,  do  we  observe  that  they  exercise  any  choice 
in  pairing.  Not  to  natural  selection,  because  we  cannot 
here,  as  in  the  case  of  vegetables,  point  to  any  benefit 
as  generally  arising  from  bright  colours  and  beautiful 
forms.  On  the  principles  of  naturalism,  therefore,  we 
are  driven  to  conclude  that  the  beauty  here  is  purely 
adventitious,  or  accidental.  Nor  need  we  be  afraid  to 
make  this  admission,  if  only  we  take  a  sufficiently  wide 
view  of  the  facts.  For,  when  we  do  take  such  a  view, 
we  find  that  beauty  here  is  by  no  means  of  invariable, 
or  even  of  general,  occurrence.  There  is  no  loveliness 
about  an  oyster  or  a  lob-worm  ;  parasites,  as  a  rule, 
are  positively  ugly,  and  they  constitute  a  good  half  of 
all  animal  species.  The  truth  seems  to  be,  when  we 
look  attentively  at  the  matter,  that  in  all  cases  where 
beauty  does  occur  in  these  lower  forms  of  animal  life, 
its  presence  is  owing  to  one  of  two  things — either 
to  the  radiate  form,  or  to  the  bright  tints.  Now, 
seeing  that  the  radiate  form  is  of  such  general 
occurrence  among  these  lower  animals — appearing 
over  and  over  again,  with  the  utmost  insistence,  even 
among  groups  widely  separated  from  one  another  by 

even  as  regards  those  that  do,  it  is  not  remarkable  that  their  chlorophyll 
should,  as  it  were,  accidentally  assume  brilliant  tints  while  breaking 
down  into  lower  grades  of  chemical  constitution.  The  case,  in  fact,  is 
exactly  parallel  to  those  in  the  animal  kingdom  which  are  considered  in 
the  ensuing  paragraphs. 


The   Theory  of  Sexual  Selection.      409 

the  latest  results  of  scientific  classification— seeing  this, 
it  becomes  impossible  to  doubt  that  the  radiate  form 
is  due  to  some  morphological  reasons  of  wide  gener- 
ality. Whether  these  reasons  be  connected  with  the 
internal  laws  of  growth,  or  to  the  external  conditions 
of  environment,  I  do  not  pretend  to  suggest.  But  I 
feel  safe  in  saying  that  it  cannot  possibly  be  due  to 
any  design  to  secure  beauty  for  its  own  sake.  The 
very  generality  of  the  radiate  form  is  in  itself  enough 
to  suggest  that  it  must  have  some  physical,  as  dis- 
tinguished from  an  aesthetic,  explanation  ;  for,  if  the 
attainment  of  beauty  had  here  been  the  object,  surely 
it  might  have  been  even  more  effectually  accomplished 
by  adopting  a  greater  variety  of  typical  forms— as,  for 
instance,  in  the  case  of  flowers. 

Coming  then,  lastly,  to  the  case  of  brilliant  tints  in 
the  lower  animals,  Mr.  Darwin  has  soundly  argued 
that  there  is  nothing  forced  or  improbable  in  the 
supposition  that  organic  compounds,  presenting  as 
they  do  such  highly  complex  and  such  varied  chemical 
constitutions,  should  often  present  brilliant  colouring 
incidentally.  Considered  merely  as  colouring,  there 
is  nothing  in  the  world  more  magnificent  than  arterial 
blood  ;  yet  here  the  colouring  is  of  purely  utilitarian 
significance.  It  is  of  the  first  importance  in  the 
chemistry  of  respiration  ;  but  is  surely  without  any 
meaning  from  an  aesthetic  point  of  view.  For  the 
colour  of  the  cheeks,  and  of  the  flesh  generally,  in 
the  white  races  of  mankind,  could  have  been  produced 
quite  as  effectually  by  the  use  of  pigment — as  in  the 
case  of  certain  monkeys.  Now  the  fact  that  in  the 
case  of  blood,  as  in  that  of  many  other  highly 
coloured  fluids  and  solids  throughout  the  animal 


4io          Darwin,  and  after  Darwin. 

kingdom,  the  colour  is  concealed,  is  surely  sufficient 
proof  that  the  colour,  if  regarded  from  an  aesthetic 
point  of  view,  is  accidental.  Therefore,  when,  as  in 
other  cases,  such  colouring  occurs  upon  the  surface, 
and  thus  becomes  apparent,  are  we  not  irresistibly 
led  to  conclude  that  its  exhibition  in  such  cases  is 
likewise  accidental,  so  far  as  any  question  of  aesthetic 
design  is  concerned  ? 

I  have  now  briefly  glanced  at  all  the  main  facts  of 
organic  nature  with  reference  to  beauty ;  and,  as  a 
result,  I  think  it  is  impossible  to  resist  the  general 
conclusion,  that  in  organic  nature  beauty  does  not 
exist  as  an  end  per  se.  All  cases  where  beauty  can 
be  pointed  to  in  organic  nature  are  seemingly  due — 
either  to  natural  selection,  acting  without  reference 
to  beauty,  but  to  utility ;  to  sexual  selection,  act- 
ing with  reference  to  the  taste  of  animals  ;  or  else 
to  sheer  accident.  And  if  this  general  conclusion 
should  be  held  to  need  any  special  verification,  is  it 
not  to  be  found  in  the  numberless  cases  where  or- 
ganic nature  not  only  fails  to  be  beautiful,  but  reveals 
itself  as  the  reverse.  Not  again  to  refer  to  the  case 
of  parasites,  what  can  be  more  unshapely  than  a 
hippopotamus,  or  more  generally  repulsive  than  a 
crocodile  ?  If  it  be  said  that  these  are  exceptions, 
and  that  the  forms  of  animals  as  a  rule  are  graceful, 
the  answer — even  apart  from  parasites — is  obvious. 
In  all  cases  where  the  habits  of  life  are  such  as  to 
render  rapid  locomotion  a  matter  of  utilitarian 
necessity,  the  outlines  of  an  animal  must  be 
graceful — else,  whether  the  locomotion  be  terrestrial, 
aerial,  or  aquatic,  it  must  fail  to  be  swift.  Hence  it 
is  only  in  such  cases  as  that  of  the  hippopotamus, 


The   Theory  of  Sexual  Selection.       411 

rhinoceros,  elephant,  crocodile,  and  so  forth,  where 
natural  selection  has  had  no  concern  in  developing 
speed,  that  the  accompanying  accident  of  gracefulness 
can  be  allowed  to  disappear.  But  if  beauty  in  or- 
ganic nature  had  been  in  itself  what  may  be  termed 
an  artistic  object  on  the  part  of  a  divine  Creator,  it 
is  absurd  to  suggest  that  his  design  in  this  matter 
should  only  have  been  allowed  to  appear  where  we 
are  able  to  detect  other  and  very  good  reasons  for  its 
appearance. 

Thus,  whether  we  look  to  the  facts  of  adaptation 
or  to  those  of  beauty,  everywhere  throughout  organic 
nature  we  meet  with  abundant  evidence  of  natural 
causation,  while  nowhere  do  we  meet  with  any  in- 
dependent evidence  of  supernatural  design.  But, 
having  led  up  to  this  conclusion,  and  having  thus 
stated  it  as  honestly  as  I  can,  I  should  like  to  finish 
by  further  stating  what,  in  my  opinion,  is  its  logical 
bearing  upon  the  more  fundamental  tenets  of  religious 
thought. 

As  I  have  already  observed  at  the  commencement 
of  this  brief  exposition,  prior  to  the  Darwinian  theory 
of  organic  evolution,  the  theologian  was  prone  to  point 
to  the  realm  of  organic  nature  as  furnishing  a  peculiarly 
rich  and  virtually  endless  store  of  facts,  all  combining 
in  their  testimony  to  the  wisdom  and  the  beneficence 
of  the  Deity.  Innumerable  adaptations  of  structures 
to  functions  appeared  to  yield  convincing  evidence 
in  favour  of  design ;  the  beauty  so  profusely  shed 
by  living  forms  appeared  to  yield  evidence,  no  less 
convincing,  of  that  design  as  beneficent.  But  both 
these  sources  of  evidence  have  now,  as  it  were,  been 


412  Darwin,  and  after  Darwin. 

tapped  at  their  fountain-head  :  the  adaptation  and 
the  beauty  are  alike  receiving  their  explanation  at 
the  hands  of  a  purely  mechanical  philosophy.  Nay, 
even  the  personality  of  man  himself  is  assailed ;  and 
this  not  only  in  the  features  which  he  shares  with 
the  lower  animals,  but  also  in  his  god-like  attributes 
of  reason,  thought,  and  conscience.  All  nature  has 
thus  been  transformed  before  the  view  of  the  present 
generation  in  a  manner  and  to  an  extent  that  has 
never  before  been  possible :  and  inasmuch  as  the 
change  which  has  taken  place  has  taken  place  in 
the  direction  of  naturalism,  and  this  to  the  extent  of 
rendering  the  mechanical  interpretation  of  nature  uni- 
versal,it  is  no  wonder  if  the  religious  mind  has  suddenly 
awakened  to  a  new  and  a  terrible  force  in  the  words  of 
its  traditional  enemy — Where  is  now  thy  God? 

This  is  not  the  place  to  discuss  the  bearings  of 
science  on  religion  l ;  but  I  think  it  is  a  place  where 
one  may  properly  point  out  the  limits  within  which  no 
such  bearings  obtain.  Now.  from  what  has  just  been 
said,  it  will  be  apparent  that  I  am  not  going  to 
minimise  the  change  which  has  been  wrought.  On 
the  contrary,  I  believe  it  is  only  stupidity  or  affecta- 
tion which  can  deny  that  the  change  in  question  is 
more  deep  and  broad  than  any  single  previous  change 
in  the  whole  history  of  human  thought.  It  is  a  fun- 
damental, a  cosmical,  a  world-transforming  change. 
Nevertheless,  in  my  opinion,  it  is  a  change  of  a  non- 
theistic,  as  distinguished  from  an  a-theistic,  kind.  It 
has  rendered  impossible  the  appearance  in  literature 
of  any  future  Paley,  Bell,  or  Chalmers  ;  but  it  has 

1  The  best  treatise  on  this  subject  is  Prof.  Le  Conte's  Evolution  and 
its  P elation  to  Religious  Thought  (Appleton  &  Co.  1888). 


The   Theory  of  Sexual  Selection.      4 1 3 

done  nothing  in  the  way  of  negativing  that  belief  in  a 
Supreme  Being  which  it  was  the  object  of  these 
authors  to  substantiate.  If  it  has  demonstrated  the 
futility  of  their  proof,  it  has  furnished  nothing  in  the 
way  of  disproof.  It  has  shown,  indeed,  that  their  line 
of  argument  was  misjudged  when  they  thus  sought 
to  separate  organic  nature  from  inorganic  as  a  theatre 
for  the  special  or  peculiar  display  of  supernatural 
design  ;  but  further  than  this  it  has  not  shown  anything. 
The  change  in  question  therefore,  although  greater  in 
degree,  is  the  same  in  kind  as  all  its  predecessors :  like 
all  previous  advances  in  cosmological  theory  which 
have  been  wrought  by  the  advance  of  science,  this 
latest  and  greatest  advance  has  been  that  of  revealing 
the  constitution  of  nature,  or  the  method  of  causation, 
as  everywhere  the  same.  But  it  is  evident  that  this 
change,  vast  and  to  all  appearance  final  though  it  be. 
must  end  within  the  limits  of  natural  causation  itself. 
The  whole  world  of  life  and  mind  may  now  have  been 
annexed  to  that  of  matter  and  energy  as  together 
constituting  one  magnificent  dominion,  which  is 
everywhere  subject  to  the  same  rule,  or  method  of 
government.  But  the  ulterior  and  ultimate  question 
touching  the  nature  of  this  government  as  mental  or 
non-mental,  personal  or  impersonal,  remains  exactly 
where  it  was.  Indeed,  this  is  a  question  which  cannot 
be  affected  by  any  advance  of  science,  further  than 
science  has  proved  herself  able  to  dispose  of  erroneous 
arguments  based  upon  ignorance  of  nature.  For  while 
the  sphere  of  science  is  necessarily  restricted  to  that 
of  natural  causation  which  it  is  her  office  to  explore, 
the  question  touching  the  nature  of  this  natural 
causation  is  one  which  as  necessarily  lies  without  the 


414          Darwin,  and  after  Darwin. 

whole  sphere  of  such  causation  itself:  therefore  it  lies 
beyond  any  possible  intrusion  by  science.  And  not 
only  so.  But  if  the  nature  of  natural  causation  be 
that  of  the  highest  order  of  known  existence,  then, 
although  we  must  evidently  be  incapable  of  conceiving 
what  such  a  Mind  is,  at  least  we  seem  capable  of 
judging  what  in  many  respects  it  is  not.  It  cannot 
be  more  than  one ;  it  cannot  be  limited  either  in 
space  or  time ;  it  cannot  be  other  than  at  least  as 
self-consistent  as  its  manifestations  in  nature  are  in- 
variable. Now,  from  the  latter  deduction  there  arises 
a  point  of  first-rate  importance  in  the  present  con- 
nexion. For  if  the  so-called  First  Cause  be  intelligent, 
and  therefore  all  secondary  causes  but  the  expression 
of  a  supreme  Will,  in  as  far  as  such  a  Will  is  self- 
consistent,  the  operation  of  all  natural  causes  must 
be  uniform,— with  the  result  that,  as  seen  by  us,  this 
operation  must  needs  appear  to  be  what  we  call 
mechanical.  The  more  unvarying  the  Will,  the  more 
unvarying  must  be  this  expression  thereof;  so  that, 
if  the  former  be  absolutely  self-consistent,  the  latter 
cannot  fail  to  be  as  reasonably  interpreted  by  the 
theory  of  mindless  necessity,  as  by  that  of  ubiquitous 
intention.  Such  being,  as  it  appears  to  me,  the  pure 
logic  of  the  matter,  the  proof  of  organic  evolution 
amounts  to  nothing  more  than  the  proof  of  a  natural 
process.  What  mode  of  being  is  ultimately  concerned 
in  this  process — or  in  what  it  is  that  this  process 
ultimately  consists — is  a  question  upon  which  science 
is  as  voiceless  as  speculation  is  vociferous. 

But,  it  may  still  be  urged,  surely  the  principle  of 
natural  selection  (with  its  terrible  basis  in  the  struggle 
for  existence)  and  the  principle  of  sexual  selection 


The   Theory  of  Sexual  Selection.       415 

(with  its  consequence  in  denying  beauty  to  be  an  end 
in  itself)  demonstrate  that,  if  there  be  design  in  nature, 
such  design  at  all  events  cannot  be  beneficent.  To 
this,  however,  I  should  again  reply  that,  just  as 
touching  the  major  question  of  design  itself,  so  as 
touching  this  minor  question  of  the  quality  of  such 
design  as  beneficent,  I  do  not  see  how  the  matter  has 
been  much  affected  by  a  discovery  of  the  principles 
before  us.  For  we  did  not  need  a  Darwin  to  tell  us 
that  the  whole  creation  groaneth  and  travaileth  to- 
gether in  pain.  The  most  that  in  this  connexion 
Darwin  can  fairly  be  said  to  have  done  is  to  have 
estimated  in  a  more  careful  and  precise  manner  than 
any  of  his  predecessors,  the  range  and  the  severity  of 
this  travail.  And  if  it  be  true  that  the  result  of  what 
may  be  called  his  scientific  analysis  of  nature  in  respect 
of  suffering  is  to  have  shown  the  law  of  suffering  even 
more  severe,  more  ubiquitous,  and  more  necessary 
than  it  had  ever  been  shown  before,  we  must  remember 
at  the  same  time  how  he  has  proved,  more  rigidly 
than  was  ever  proved  before,  that  suffering  is  a 
condition  to  improvement — struggle  for  life  being  the 
raison  d'etre  of  higher  life,  and  this  not  only  in  the 
physical  sphere,  but  also  in  the  mental  and  moral. 

Lastly,  if  it  be  said  that  the  choice  of  such  a  method, 
whereby  improvement  is  only  secured  at  the  cost  of 
suffering,  indicates  a  kind  of  callousness  on  the  part 
of  an  intelligent  Being  supposed  to  be  omnipotent,  I 
confess  that  such  does  appear  to  me  a  legitimate 
conclusion— subject,  however,  to  the  reservation  that 
higher  knowledge  might  displace  it.  For,  as  far  as 
matters  are  now  actually  presented  to  the  unbiased 
contemplation  of  a  human  mind,  this  provisional 


416          Darwin,  and  after  Darwin. 

inference  appears  to  me  unavoidable — namely,  that 
if  the  world  of  sentient  life  be  due  to  an  Omnipotent 
Designer,  the  aim  or  motive  of  the  design  must  have 
been  that  of  securing  a  continuous  advance  of  animal 
improvement,  without  any  regard  at  all  to  animal  suf- 
fering. For  I  own  it  does  not  seem  to  me  compatible 
with  a  fair  and  honest  exercise  of  our  reason  to  set  the 
sum  of  animal  happiness  over  against  the  sum  of  animal 
misery,  and  then  to  allege  that,  in  so  far  as  the  former 
tends  to  balance— or  to  over-balance — the  latter,  thus 
far  is  the  moral  character  of  the  design  as  a  whole 
vindicated.  Even  if  it  could  be  shown  that  the  sum  of 
happiness  in  thebrute  creation  considerably  preponder- 
ates over  that  of  unhappiness — which  is  the  customary 
argument  of  theistic  apologists, — we  should  still  remain 
without  evidence  as  to  this  state  of  matters  having 
formed  any  essential  part  of  the  design.  On  the  other 
hand,  we  should  still  be  in  possession  of  seemingly  good 
evidence  to  the  contrary.  For  it  is  clearly  a  condition 
to  progress  by  survival  of  the  fittest,  that  as  soon  as 
organisms  become  sentient  selection  must  be  ex- 
ercised with  reference  to  sentiency ;  and  this  means 
that,  if  further  progress  is  to  take  place,  states  of 
sentiency  must  become  so  organized  with  reference  to 
habitual  experience  of  the  race,  that  pleasures  and 
pains  shall  answer  respectively  to  states  of  agreement 
and  disagreement  with  the  sentient  creature's  environ- 
ment. Those  animals  which  found  pleasure  in  what 
was  deleterious  to  life  would  not  survive,  while  those 
which  found  pleasure  in  what  was  beneficial  to  life 
would  survive ;  and  so  eventually,  in  every  species  of 
animal,  states  of  sentiency  as  agreeable  or  disagreeable 
must  approximately  correspond  with  what  is  good  for 


The   Theory  of  Sexual  Selection.       4 1 7 

the  species  or  bad  for  the  species.  Indeed,  we  may 
legitimately  surmise  that  the  reason  why  sentiency 
(and,  a  fortiori,  conscious  volition)  has  ever  appeared 
upon  the  scene  at  all,  has  been  because  it  furnishes — 
through  this  continuously  selected  adjustment  of  states 
of  sentiency  to  states  of  the  sentient  organism — so 
admirable  a  means  of  securing  rapid,  and  often  refined, 
adjustments  by  the  organism  to  the  habitual  conditions 
of  its  life  *.  But,  if  so,  not  only  is  this  state  of  matters 
a  condition  to  progress  in  the  future ;  it  is  further, 
and  equally,  a  consequence  of  progress  in  the  past. 

However,  be  this  as  it  may,  from  all  that  has  gone 
before  does  it  not  become  apparent  that  pleasure  or 
happiness  on  the  one  hand,  and  pain  or  misery  on  the 
other,  must  be  present  in  sentient  nature?  And  so 
long  as  they  are  both  seen  to  be  equally  necessary 
under  the  process  of  evolution  by  natural  selection, 
we  have  clearly  no  more  reason  to  regard  the  pleasure 
than  the  pain  as  an  object  of  the  supposed  design. 
Rather  must  we  see  in  both  one  and  the  same 
condition  to  progress  under  the  method  of  natural 
causation  which  is  before  us  ;  and  therefore  I  cannot 
perceive  that  it  makes  much  difference — so  far  as  the 
argument  for  beneficence  is  concerned — whether  the 
pleasures  of  animals  outweigh  their  pains,  or  vice 
vcrsd. 

Upon  the  whole,  then,  it  seems  to  me  that  such 
evidence  as  we  have  is  against  rather  than  in  favour 
of  the  inference,  that  if  design  be  operative  in  animate 
nature  it  has  reference  to  animal  enjoyment  or  well- 
being,  as  distinguished  from  animal  improvement  or 
evolution.  And  if  this  result  should  be  found  dis- 

1  See  Mental  Evolution  in  Animals,  pp.  lio-m. 
*  EC 


41 8  Darwin,  and  after  Darwin. 

tasteful  to  the  religious  mind — if  it  be  felt  that  there 
is  no  desire  to  save  the  evidences  of  design  unless 
they  serve  at  the  same  time  to  testify  to  the  nature  of 
that  design  as  beneficent, —  I  must  once  more  observe 
that  the  difficulty  thus  presented  to  theism  is  not  a 
difficulty  of  modern  creation.  On  the  contrary,  it  has 
always  constituted  the  fundamental  difficulty  with 
which  natural  theologians  have  had  to  contend.  The 
external  world  appears,  in  this  respect,  to  be  at 
variance  with  our  moral  sense  ;  and  when  the  an- 
tagonism is  brought  home  to  the  religious  mind,  it 
must  ever  be  with  a  shock  of  terrified  surprise.  It 
has  been  newly  brought  home  to  us  by  the  general- 
izations of  Darwin  ;  and  therefore,  as  I  said  at  the 
beginning,  the  religious  thought  of  our  generation 
has  been  more  than  ever  staggered  by  the  question — 
Where  is  now  thy  God  ?  But  I  have  endeavoured  to 
show  that  the  logical  standing  of  the  case  has  not 
been  materially  changed ;  and  when  this  cry  of 
Reason  pierces  the  heart  of  Faith,  it  remains  for 
Faith  to  answer  now,  as  she  has  always  answered 
before — and  answered  with  that  trust  which  is  at 
once  her  beauty  and  her  life — Verily  thou  art  a  God 
that  hidest  thyself. 


APPENDIX  AND  NOTES 


E  e  2 


APPENDIX  TO  CHAPTER  V. 

ON   OBJECTIONS   WHICH   HAVE   BEEN  BROUGHT  AGAINST  THE 

THEORY  OF  ORGANIC  EVOLUTION  ON  GROUNDS  OF 

PALEONTOLOGY. 

WHILE  stating  in  the  text,  and  in  a  necessarily  general  way, 
the  evidence  which  is  yielded  by  palaeontology  to  the  theory 
of  organic  evolution,  I  have  been  desirous  of  not  overstating 
it.  Therefore,  in  the  earlier  paragraphs  of  the  chapter, 
which  deal  with  the  most  general  heads  of  such  evidence,  I 
introduced  certain  qualifying  phrases;  and  I  will  now  give 
the  reasons  which  led  me  to  do  so. 

Of  all  the  five  biological  sciences  which  have  been  called 
into  evidence — viz.  those  of  Classification,  Morphology, 
Embryology,  Palaeontology,  and  Geographical  Distribution — 
it  is  in  the  case  of  palaeontology  alone  that  any  important 
or  professional  opinions  still  continue  to  be  unsatisfied. 
Therefore,  in  order  that  justice  may  be  done  to  this  line  of 
dissent,  I  have  thought  it  better  to  deal  with  the  matter  in 
a  separate  Appendix,  rather  than  to  hurry  it  over  in  the 
text.  And,  as  all  the  difficulties  or  objections  which  have 
been  advanced  against  the  theory  of  evolution  on  grounds  of 
palaeontology  must  vary,  as  to  their  strength,  \\ilh  the  estimate 
which  is  taken  touching  the  degree  of  imperfection  of  the 
geological  record,  I  will  begin  by  adding  a  few  paragraphs  to 
what  has  already  been  said  in  the  text  upon  this  subject. 

First,  then,  as  to  the  difficulties  in  the  way  of  fossils  being 


422          Darwin,  and  after  Darwin. 

formed  at  all.  We  have  already  noticed  in  the  text  that  it  is 
only  the  more  or  less  hard  parts  of  organisms  which  under 
any  circumstances  can  be  fossilized;  and  even  the  hardest 
parts  quickly  disintegrate  if  not  protected  from  the  weather 
on  land,  or  from  the  water  on  the  sea-bottom.  Moreover,  as 
Darwin  says,  "we  probably  take  a  quite  erroneous  view 
when  we  assume  that  sediment  is  being  deposited  over 
nearly  the  whole  bed  of  the  sea,  at  a  rate  sufficiently  quick 
to  embed  and  preserve  fossil  remains.  Throughout  an 
enormously  large  proportion  of  the  ocean,  the  bright  blue 
tint  of  the  water  bespeaks  its  purity.  The  many  cases  on 
record  of  a  formation  conformably  covered,  after  an  immense 
interval  of  time,  by  another  and  a  later  formation,  without  the 
underlying  bed  having  suffered  in  the  interval  any  wear  and 
tear,  seem  explicable  only  on  the  view  of  the  bottom  of  the 
sea  not  rarely  lying  for  ages  in  an  unaltered  condition." 
Next,  as  regards  littoral  animals,  he  shows  the  difficulty 
which  they  must  have  in  becoming  fossils,  and  gives  a 
striking  example  in  several  of  the  existing  species  of  a  sub- 
family of  cirripedes  (Chthamaltnce),  "  which  coat  the  rocks  all 
over  the  world  in  infinite  numbers,"  yet,  with  the  exception  of 
one  species  which  inhabits  deep  water,  no  vestige  of  any  of 
them  has  been  found  in  any  tertiary  formation,  although  it  is 
known  that  the  genus  Chthamalus  existed  through  the  Chalk 
period.  Lastly,  "  with  respect  to  the  terrestrial  productions 
which  lived  through  the  secondary  and  palaeozoic  periods,  it 
is  superfluous  to  state  our  evidence  is  fragmentary  in  an 
extreme  degree.  For  instance,  until  recently  not  a  land 
shell  was  known  belonging  to  either  of  these  vast  periods," 
with  one  exception;  while,  "in  regard  to  mammiferous 
remains,  a  glance  at  the  historical  table  in  Lyell's  Manual 
will  bring  home  the  truth,  how  accidental  and  rare  has  been 
their  preservation,  far  better  than  pages  of  detail.  Nor  is  their 
rarity  surprising,  when  we  remember  how  large  a  proportion 
of  the  bones  of  tertiary  mammals  have  been  discovered  either 


Appendix  to  Chapter  V.  423 

in  caves  or  in  lacustrine  deposits;  and  that  not  a  cave  or 
true  lacustrine  bed  is  known  belonging  to  the  age  of  our 
secondary  or  palaeozoic  formations." 

But  perhaps  of  even  more  importance  than  all  these  known 
causes  which  prevent  the  formation  of  fossils,  is  the  existence 
of  unknown  causes  which  make  for  the  same  result.  For 
example,  the  Flysch-formation  is  a  formation  of  several 
thousand  feet  in  thickness  (as  much  as  6000  in  some  places), 
and  it  extends  for  at  least  300  miles  from  Vienna  to 
Switzerland ;  moreover,  it  consists  of  shale  and  sandstone. 
Therefore,  alike  in  respect  of  time,  space,  and  character,  it  is 
just  such  a  formation  as  we  should  expect  to  find  highly  rich 
in  fossils;  yet,  "although  this  great  mass  has  been  most 
carefully  searched,  no  fossils,  except  a  few  vegetable  remains, 
have  been  found." 

So  much  then  for  the  difficulty,  so  to  speak,  which  nature 
experiences  in  the  manufacture  of  fossils.  Probably  not  one 
per  cent,  of  the  species  of  animals  which  have  inhabited  the 
earth  has  left  a  single  individual  as  a  fossil,  whereby  to  record 
its  past  existence. 

But  of  even  more  importance  than  this  difficulty  of  making 
fossils  in  the  first  instance,  is  the  difficulty  of  preserving  them 
when  they  are  made.  The  vast  majority  of  fossils  have  been 
formed  under  water,  and  a  large  proportional  number  of 
these— whether  the  animals  were  marine,  terrestrial,  or 
inhabitants  of  fresh  water— have  been  formed  in  sedimentary 
deposits  either  of  sand,  gravel,  or  other  porous  material. 
Now.  where  such  deposits  have  been  afterwards  raised  into 
the  air  for  any  considerable  time — and  this  has  been  more  or 
less  the  case  with  all  deposits  which  are  available  for  explora- 
tion— their  fossiliferous  contents  will  have  been,  as  a  general 
rule,  dissolved  by  the  percolation  of  rain-water  charged  with 
carbonic  acid.  Similarly,  sea-water  has  recently  been  found 
to  be  a  surprisingly  strong  solvent  of  calcareous  material: 
hence,  Saturn-like,  the  ocean  devours  her  own  pio&eny 


424          Darwin,  and  after  Darwin. 

as  far  as  shells  and  bones  of  all  kinds  are  concerned — 
and  this  to  an  extent  of  which  we  have  probably  no  adequate 
conception. 

Of  still  greater  destructive  influence,  however,  than  these 
solvent  agencies  in  earth  and  sea,  are  the  erosive  agencies  of 
both.  Any  one  who  watches  the  pounding  of  the  waves 
upon  the  shore ;  who  then  observes  the  effect  of  it  upon  the 
rocks  broken  into  shingle,  and  on  the  shingle  reduced  to 
sand ;  who,  looking  behind  him  at  the  cliffs,  sees  there  the 
evidence  of  the  gradual  advance  of  this  all-pulverising  power 
— an  advance  so  gradual  that  no  yard  of  it  is  accomplished 
until  within  that  yard  the  "  white  teeth  "  have  eaten  well  into 
the  "  bowels  of  the  earth  " ;  who  then  reflects  that  this  process 
is  going  on  simultaneously  over  hundreds  of  thousands  of  miles 
of  coast-lines  throughout  the  world  ;  and  \vho  finally  extends 
his  mental  vision  from  space  to  time,  by  trying  dimly  to 
imagine  what  this  ever-roaring  monster  must  have  consumed 
during  the  hundreds  of  millions  of  years  that  slowly  rising 
and  slowly  sinking  continents  have  exposed  their  whole  areas 
to  her  jaws ;  whoever  thus  observes  and  thus  reflects  must  be 
a  dull  man,  if  he  does  not  begin  to  feel  that  in  the  presence 
of  such  a  destroyer  as  this  we  have  no  reason  to  wonder  at  a 
frequent  silence  in  the  testimony  of  the  rocks. 

But  although  the  erosive  agency  of  the  sea  is  thus  so 
inconceivably  great,  it  is  positively  small  if  compared  with 
erosive  agencies  on  land.  The  constant  action  of  rain,  wind, 
and  running  water,  in  wearing  down  the  surfaces  of  all  lands 
into  "the  dust  of  continents  to  be";  the  disintegrating 
effects  on  all  but  the  very  hardest  rocks  of  winter  frosts 
alternating  with  summer  heats;  the  grinding  power  of  ice 
in  periods  of  glacialion;  and  last,  but  not  least,  the  whole- 
sale melting  up  of  sedimentary  formations  whenever  these 
have  sunk  for  any  considerable  distance  beneath  the  earth's 
surface : — all  these  agencies  taken  together  constitute  so 
prodigious  a  sum  of  energies  combined  through  immeasure- 


Appendix  to  Chapter  V.  425 

able  ages  in  their  common  work  of  destruction,  that  when 
we  try  to  realise  what  it  must  amount  to,  we  can  scarcely 
fail  to  wonder,  not  that  the  geological  record  is  highly  im- 
perfect, but  that  so  much  of  the  record  has  survived  as  we 
find  to  have  been  the  case.  And,  if  we  add  to  these  erosive 
and  solvent  agencies  on  land  the  erosive  and  solvent  agencies 
of  the  sea,  we  may  almost  begin  to  wonder  that  anything 
deserving  the  name  of  a  geological  record  is  in  existence 
at  all. 

That  such  estimates  of  the  destructive  powers  of  nature 
are  not  mere  matters  of  speculative  reasoning  may  be  amply 
shown  by  stating  one  single  fact,  which,  like  so  many  others 
where  the  present  subject  is  concerned,  we  owe  to  the 
generalizations  of  Darwin.  Plutonic  rocks,  being  those  which 
have  emerged  from  subterranean  heat  of  melting  intensity, 
must  clearly  at  some  time  or  another  have  lain  beneath  the 
whole  thickness  of  sedimentary  deposits,  which  at  that  time 
occupied  any  part  of  the  earth's  surface  where  we  now  find 
the  Plutonic  rocks  exposed  to  view.  Or,  in  other  words, 
wherever  we  now  find  Plutonic  rocks  at  the  surface  of  the  earth, 
we  must  conclude  that  all  the  sedimentary  rocks  by  which  they 
were  covered  when  in  a  molten  state  have  since  been  entirely 
destroyed ;  several  vertical  miles  of  the  only  kinds  of  rocks 
in  which  fossils  can  possibly  occur  must  in  all  such  cases 
have  been  abolished  in  Mo.  Now,  in  many  parts  of  the 
world  metamorphic  rocks— which  have  thus  gradually  risen 
from  Plutonic  depths,  while  miles  of  various  other  rock- 
formations  have  been  removed  from  their  now  exposed 
surfaces — cover  immense  areas,  and  therefore  testify  by  their 
present  horizontal  range,  no  less  than  by  their  previously 
vertical  depth,  to  the  enormous  scale  on  which  a  total 
destruction  has  taken  place  of  everything  that  once  lay 
above  them.  For  instance,  the  granitic  region  of  Parime  is 
at  least  nineteen  times  the  size  of  Switzerland ;  a  similar 
region  south  of  the  Amazon  is  probably  larger  than  France, 


426          Darwin,  and  after  Darwin. 

Spain,  Italy,  and  Great  Britain  all  put  together;  and,  more 
remarkable  still,  over  the  area  of  the  United  States  and 
Canada,  granitic  rocks  exceed  in  the  proportion  of  19  to  \z\ 
the  whole  of  the  newer  Palaeozoic  formations.  Lastly,  after 
giving  these  examples,  Darwin  adds  the  important  con- 
sideration, that  "in  many  regions  the  metamorphic  and 
granitic  rocks  would  be  found  much  more  widely  extended 
than  they  appear  to  be,  if  all  the  sedimentary  beds  were 
removed  which  rest  unconformably  on  them,  and  which 
could  not  have  formed  part  of  the  original  mantle  under 
which  they  were  crystallized." 

The  above  is  a  brief  condensation  of  the  already  condensed 
statement  which  Darwin  has  given  of  the  imperfection  of  the 
geological  record  ;  but  I  think  it  is  enough  to  show,  in  a 
general  way,  how  precarious  must  be  the  nature  of  any 
objections  to  the  theory  of  evolution  which  are  founded 
merely  upon  the  silence  of  palaeontology  in  cases  where,  if 
the  record  were  anything  like  complete,  we  should  be  entitled 
to  expect  from  it  some  positive  information.  But,  as  we 
have  seen  in  the  text,  imperfect  though  the  record  be,  in  as 
far  as  it  furnishes  positive  information  at  all,  this  is  well-nigh 
uniformly  in  favour  of  the  theory ;  and  therefore,  even  on 
grounds  of  palaeontology  alone,  it  appears  to  me  that  Darwin 
is  much  too  liberal  where  he  concludes  his  discussion  by 
saying, — "  Those  who  believe  that  the  geological  record  is 
in  any  degree  perfect,  will  undoubtedly  at  once  reject  the 
theory."  If  in  any  measure  reasonable,  such  persons  ought 
rather  to  examine  their  title  to  such  a  belief;  and  even  if  they 
disregard  the  consensus  of  testimony  which  is  yielded  by  all 
the  biological  sciences  to  the  theory  of  evolution,  they  ought 
at  least  to  hold  their  judgment  in  suspense  until  they  shall 
have  not  only  set  against  the  apparently  negative  testimony 
which  is  yielded  by  geology  its  unquestionably  positive  testi- 
mony, but  also  well  considered  the  causes  which  may — or 
rather  must — have  so  gravely  impaired  the  geological  record. 


Appendix  to  Chapter  V.  427 

However,  be  this  as  it  may,  I  will  now  pass  on  to  con- 
sider the  difficulties  and  objections  which  have  been  brought 
against  the  theory  on  grounds  of  palaeontology. 

These  may  be  classified  under  four  heads.  First,  the  ab- 
sence of  varietal  links  between  allied  species ;  second,  the 
sudden  appearance  of  whole  groups  of  species — not  only  as 
genera  and  families,  but  even  sometimes  as  orders  and  classes 
—without  any  forms  leading  up  to  them ;  third,  the  occurrence 
of  highly  organized  types  at  much  lower  levels  of  geological 
strata  than  an  evolutionist  would  antecedently  expect ;  and, 
fourth,  the  absence  of  fossils  of  any  kind  lower  down  than 
the  Cambrian  strata. 

Now  all  these  objections  depend  on  estimates  of  the  im- 
perfection of  the  geological  record  much  lower  than  that 
which  is  formed  by  Darwin.  Therefore  I  have  arranged  the 
objections  in  their  order  of  difficulty  in  this  respect,  or  in  the 
order  that  requires  successively  increasing  estimates  of  the 
imperfection  of  the  record,  if  they  are  to  be  successively 
answered. 

I  think  that  the  first  of  them  has  been  already  answered  in 
the  text,  by  showing  that  even  a  very  moderate  estimate  of  the 
imperfection  of  the  record  is  enough  to  explain  why  interme- 
diate varieties,  connecting  allied  species^  are  but  comparatively 
seldom  met  with.  Moreover  it  \\  as  shown  that  in  some  cases, 
where  shells  are  concerned,  remarkably  well-connected  series 
of  such  varieties  have  been  met  with.  And  the  same  applies 
to  species  and  genera  in  certain  other  cases,  as  in  the 
equine  family. 

But  no  doubt  a  greater  difficulty  arises  where  whole  groups 
of  species  and  genera,  or  even  families  and  orders,  appear  to 
arise  suddenly,  without  anything  leading  up  to  them.  Even 
this  the  second  difficulty,  however,  admits  of  being  fully  met, 
when  we  remember  that  in  very  many  cases  it  has  been 
proved,  quite  apart  from  the  theory  of  descent,  that  super- 
jacent  formations  have  been  separated  from  one  another  by 


428  Darwin,  and  after  Darwin. 

wide  intervals  of  time.  And  even  although  it  often  happens 
that  intermediate  deposits  which  are  absent  in  one  part  of 
the  world  are  present  in  another,  we  have  no  right  to  assume 
that  such  is  always  the  case.  Besides,  even  if  it  were,  we 
should  have  no  right  further  to  assume  that  the  faunas  of 
widely  separated  geographical  areas  were  identical  during  the 
time  represented  by  the  intermediate  formation.  Yet,  unless 
they  were  identical,  we  should  not  expect  the  fossils  of  the 
intermediate  formation,  where  extant,  to  yield  evidence  of 
what  the  fossils  would  have  been  in  this  same  formation  else- 
where, had  it  not  been  there  destroyed.  Now,  as  a  matter  of 
fact,  "  geological  formations  of  each  region  are  almost  in- 
variably intermittent " ;  and  although  in  many  cases  a  more 
or  less  continuous  record  of  past  forms  of  life  can  be 
obtained  by  comparing  the  fossils  of  one  region  and  forma- 
tion with  those  of  another  region  and  adjacent  formations, 
it  is  evident  (from  what  we  know  of  the  present  geographical 
distribution  of  plants  and  animals)  that  not  a  few  cases  there 
must  have  been  where  the  interruption  of  the  record  in 
one  region  cannot  be  made  good  by  thus  interpolating  the 
fossils  of  another  region.  And  we  must  remember  it  is 
by  selecting  the  cases  where  this  cannot  be  done  that  the 
objection  before  us  is  made  to  appear  formidable.  In  other 
words,  unless  whole  groups  of  new  species  which  are  un- 
known in  formation  A  appear  suddenly  in  formation  C 
of  one  region  (X),  where  the  intermediate  formation  B  is 
absent ;  and  unless  in  some  other  region  (Y),  where  B  is 
present,  the  fossiliferous  contents  of  B  fail  to  supply  the  fossil 
ancestry  of  the  new  species  in  A  (X) ;  unless  such  a  state  of 
matters  is  found  to  obtain,  the  objection  before  us  has  nothing 
to  say.  But  at  best  this  is  negative  evidence  ;  and,  in  order 
to  consider  it  fairly,  we  ought  to  set  against  it  the  cases  where 
an  interposition  of  fossils  found  in  B  (Y)  does  furnish  the  fossil 
ancestry  of  what  would  otherwise  have  been  an  abrupt  appear- 
ance oi  whole  groups  of  new  species  in  A  (X).  Now  such 


Appendix  to  Chapter  V.  429 

cases  are  neither  few  nor  unimportant,  and  therefore  they 
deprive  the  objection  of  the  force  it  would  have  had  if  the 
selected  cases  to  the  contrary  were  the  general  rule. 

In  addition  to  these  considerations,  the  following,  some  of 
which  are  of  a  more  special  kind,  appear  to  me  so  important 
that  I  will  quote  them  almost  in  exlenso. 

We  continually  forget  how  large  the  world  is,  compared  with 
the  area  over  which  our  geological  formations  have  been  care- 
fully examined :  we  forget  that  groups  of  species  may  elsewhere 
have  long  existed,  and  have  slowly  multiplied,  before  they  in- 
vaded the  ancient  archipelagoes  of  Europe  and  the  United  States. 
We  do  not  make  due  allowance  for  the  intervals  of  time  which 
have  elapsed  between  our  consecutive  formations,— longer  per- 
haps in  many  cases  than  the  time  required  for  the  accumulation 
of  each  formation.  These  intervals  will  have  given  time  for  the 
multiplication  of  species  from  some  one  parent  form  ;  and,  in 
the  succeeding  formation,  such  groups  of  species  will  appear  as 
if  suddenly  created. 

I  may  here  recall  a  remark  formerly  made,  namely,  that  it 
might  require  a  long  succession  of  ages,  to  adapt  an  organism 
to  some  new  and  peculiar  line  of  life,  for  instance,  to  fly  through 
the  air ;  and  consequently  that  the  transitional  form  would  often 
long  remain  confined  to  some  one  region ;  but  that,  when  this 
adaptation  had  once  been  effected,  and  a  few  species  had  thus 
acquired  a  great  advantage  over  other  organisms,  a  compara- 
tively short  time  would  be  necessary  to  produce  many  divergent 
forms,  which  would  spread  rapidly  and  widely  throughout  the 
world. .  .  . 

In  geological  treatises,  published  not  many  years  ago, 
mammals  were  always  spoken  of  as  having  abruptly  come  in  at 
the  commencement  of  the  tertiary  series.  And  now  one  of  the 
richest  known  accumulations  of  fossil  mammals  belongs  to  the 
middle  of  the  secondary  series ;  and  true  mammals  have  been 
discovered  in  the  new  red  sandstone  at  nearly  the  commence- 
ment of  this  great  series.  Cuvier  used  to  urge  that  no  monkey 
occurred  in  any  tertiary  stratum ;  but  now  extinct  species  have 
been  discovered  in  India,  South  America,  and  in  Europe  as  far 


430          Darwin,  and  after  Darwin, 

back  as  the  miocene  stage.  Had  it  not  been  for  the  rare  accident 
of  the  preservation  of  footsteps  in  the  new  red  sandstone  of  the 
United  States,  who  would  have  ventured  to  suppose  that,  no 
less  than  at  least  thirty  kinds  of  bird-like  animals,  some  of 
gigantic  size,  existed  during  that  period  ?  Not  a  fragment 
of  bone  has  been  discovered  in  these  beds.  Not  long  ago 
palaeontologists  maintained  that  the  whole  class  of  birds  came 
suddenly  into  existence  during  the  eocene  period ;  but  now 
we  know,  on  the  authority  of  Professor  Owen,  that  a  bird 
certainly  lived  during  the  deposition  of  the  upper  green-sand. 
And  still  more  recently  that  strange  bird,  the  Archeopteryx  .  .  . 
has  been  discovered  in  the  oolitic  slates  of  Solenhofen.  Hardly 
any  recent  discovery  shows  more  forcibly  than  this,  how  little 
we  as  yet  know  of  the  former  inhabitants  of  the  world. 

I  may  give  another  instance,  which,  from  having  passed 
under  my  own  eyes,  has  much  struck  me.  In  a  memoir  on 
Fossil  Sessile  Cirripedes,  I  stated  that,  from  the  number  of 
existing  and  extinct  tertiary  species  ;  from  the  extraordinary 
abundance  of  the  individuals  of  many  species  all  over  the  world 
from  the  Arctic  regions  to  the  equator,  inhabiting  various  zones 
of  depths  from  the  upper  tidal  limits  to  50  fathoms ;  from  the 
perfect  manner  in  which  specimens  are  preserved  in  the  oldest 
tertiary  beds;  from  the  ease  with  which  even  a  fragment  of 
a  valve  can  be  recognized ;  from  all  these  circumstances,  I 
inferred  that  had  sessile  cirripedes  existed  during  the  secondary 
periods,  they  would  certainly  have  been  preserved  and  dis- 
covered ;  and  as  not  one  species  had  then  been  discovered 
in  beds  of  this  age,  I  concluded  that  this  great  group  had  been 
suddenly  developed  at  the  commencement  of  the  tertiary  series. 
This  was  a  sore  trouble  to  me,  adding  as  I  thought  one  more 
instance  of  the  abrupt  appearance  of  a  great  group  of  species. 
But  my  work  had  hardly  been  published,  when  a  skilful  palaeon- 
tologist, M.  Bosquet,  sent  me  a  drawing  of  a  perfect  specimen  of 
an  unmistakeable  sessile  cirripede,  which  he  had  himself  ex- 
tracted from  the  chalk  of  Belgium.  And,  as  if  to  make  the  case 
as  striking  as  possible,  this  sessile  cirripede  was  a  Chthamalus, 
a  very  common,  large,  and  ubiquitous  genus,  of  which  not  one 
specimen  has  as  yet  been  found  even  in  any  tertiary  stratum. 
Still  more  recently,  a  Pyrgoma,  a  member  of  a  distinct  sub- 


Appendix  to  Chapter  V.  431 

family  of  sessile  cirripedes,  has  been  discovered  by  Mr.  Woodward 
in  the  upper  chalk ;  so  that  we  now  have  abundant  evidence  of 
the  existence  of  this  group  of  animals  during  the  secondary 
period. 

The  case  most  frequently  insisted  on  by  palaeontologists  of  the 
apparently  sudden  appearance  of  a  whole  group  of  species,  is  that 
of  the  teleostean  fishes,  low  down,  according  to  Agassiz,  in  the 
Chalk  period.  This  group  includes  the  large  majority  of  existing 
species.  But  certain  Jurassic  and  Triassic  forms  are  now 
commonly  admitted  to  be  teleostean  ;  and  even  some  palaeozoic 
forms  have  been  thus  classed  by  one  high  authority.  If  the 
teleosteans  had  really  appeared  suddenly  in  the  northern 
hemisphere,  the  fact  would  have  been  highly  remarkable ;  but 
it  would  not  have  formed  an  insuperable  difficulty,  unless 
it  could  likewise  have  been  shown  that  at  the  same  period 
the  species  were  suddenly  and  simultaneously  developed  in 
other  quarters  of  the  world.  It  is  almost  superfluous  to  re- 
mark that  hardly  any  fossil  fish  are  known  from  south  of 
the  equator ;  and  by  running  through  Pictet's  Palaeontology  it 
will  be  seen  that  very  few  species  are  known  from  several 
formations  in  Europe.  Some  few  families  of  fish  now  have 
a  confined  range  ;  the  teleostean  fish  might  formerly  have  had 
a  similarly  confined  range,  and  after  having  been  largely 
developed  in  some  one  sea,  might  have  spread  widely.  Nor 
have  we  any  right  to  suppose  that  the  seas  of  the  world  have 
always  been  so  freely  open  from  south  to  north  as  they  are 
at  present.  Even  at  this  day,  if  the  Malay  Archipelago  were 
converted  into  land,  the  tropical  parts  of  the  Indian  Ocean 
would  form  a  large  and  perfectly  enclosed  basin,  in  which  any 
great  group  of  marine  animals  might  be  multiplied ;  and  here 
they  would  remain  confined,  until  some  of  the  species  became 
adapted  to  a  cooler  climate,  and  were  enabled  to  double  the 
southern  capes  of  Africa  or  Australia,  and  thus  reach  other  and 
distant  seas. 

From  these  considerations,  from  our  ignorance  of  the  geology 
of  other  countries  beyond  the  confines  of  Europe  and  the  United 
States;  and  from  the  revolution  in  our  palaeontological  knowledge 
effected  by  the  discoveries  of  the  last  dozen  years,  it  seems  to 
me  to  be  about  as  rash  to  dogmatize  on  the  succession  of  organic 


432  Darwin,  and  after  Darwin. 

forms  throughout  the  world,  as  it  would  be  for  a  naturalist  to 
land  for  five  minutes  on  some  one  barren  point  in  Australia, 
and  then  to  discuss  the  number  and  range  of  its  productions  *. 


In  view  of  all  the  foregoing  facts  and  considerations,  it 
appears  to  me  that  the  second  difficulty  on  our  list  is  com- 
pletely answered.  Indeed,  even  on  a  moderate  estimate  of 
the  imperfection  of  the  geological  record,  the  wonder  would 
have  been  if  many  cases  had  not  occurred  where  groups  of 
species  present  the  fictitious  appearance  of  having  been 
suddenly  and  simultaneously  created  in  the  particular  forma- 
tions where  their  remains  now  happen  to  be  observable. 

Turning  next  to  the  third  objection,  there  cannot  be  any 
question  that  every  here  and  there  in  the  geological  series 
animals  occur  of  a  much  higher  grade  zoologically  than  the 
theory  of  evolution  would  have  expected  to  find  in  the  strata 
where  they  are  found.  At  any  rate,  speaking  for  myself,  I 
should  not  have  antecedently  expected  to  meet  with  such 
highly  differentiated  insects  as  butterflies  and  dragonflies  in 
the  middle  of  the  Secondaries :  still  less  should  I  have  ex- 
pected to  encounter  beetles,  cockroaches,  spiders,  and  May- 
flies in  the  upper  and  middle  Primaries — not  to  mention  an 
insect  and  a  scorpion  even  in  the  lower.  And  I  think 
the  same  remark  applies  to  a  whole  sub-kingdom  in  the  case 
of  Vertebrata.  For  although  it  is  only  the  lowest  class  of 
the  sub-kingdom  which,  so  far  as  we  positively  know,  was 
represented  in  the  Devonian  and  Silurian  formations,  we 
must  remember,  on  the  one  hand,  that  even  a  cartilaginous 
or  ganoid  fish  belongs  to  the  highest  sub-kingdom  of  the 
animal  series ;  and,  on  the  other  hand,  that  such  animals  are 
thus  proved  to  have  abounded  in  the  very  lowest  strata 
where  there  is  good  evidence  of  there  having  been  any  forms  of 
life  at  alL  Lastly,  the  fact  that  Marsupials  occur  in  the  Trias, 

1  Origin  of  Species,  282-5. 


Appendix  to  Chapter   V.  433 

coupled  with  the  fact  that  the  still  existing  Monotremata 
are  what  may  be  termed  animated  fossils,  referring  us  by  their 
lowly  type  of  organization  to  some  period  enormously  more 
remote, — these  facts  render  it  practically  certain  that  some 
members  of  this  very  highest  class  of  the  highest  sub-kingdom 
must  have  existed  far  back  in  the  Primaries. 

These  things,  I  say,  I  should  not  have  expected  to  find, 
and  I  think  all  other  evolutionists  ought  to  be  prepared  to 
make  the  same  acknowledgment.  But  as  these  things  have 
been  found,  the  only  possible  way  of  accounting  for  them  on 
evolutionary  principles  is  by  supposing  that  the  geological 
record  is  even  more  imperfect  than  we  needed  to  suppose  in 
order  to  meet  the  previous  objections.  I  cannot  see,  however, 
why  evolutionists  should  be  afraid  to  make  this  acknowledg- 
ment. For  I  do  not  know  any  reason  which  would  lead  us  to 
suppose  that  there  is  any  common  measure  between  the 
distances  marked  on  our  tables  of  geological  formations,  and 
the  times  which  those  distances  severally  represent.  Let  the 
reader  turn  to  the  table  on  page  163,  and  then  let  him  say 
why  the  30,000  feet  of  so-called  Azoic  rocks  may  not  represent 
a  greater  duration  of  time  than  does  the  thickness  of  all  the 
Primary  rocks  above  them  put  together.  For  my  own  part  I 
believe  that  this  is  probably  the  case,  looking  to  the  enormous 
ages  during  which  these  very  early  formaiions  must  have  been 
exposed  to  destructive  agencies  of  all  kinds,  now  at  one  time 
and  now  at  another,  in  different  parts  of  the  world.  And, 
of  course,  we  are  without  any  means  of  surmising  what 
ranges  of  time  are  represented  by  the  so-called  Primeval 
rocks,  for  the  simple  reason  that  they  are  non-sedimentary, 
and  non-sedimentary  rocks  cannot  be  expected  to  contain 
fossils. 

But,  it  will  be  answered,  the  30,000  feet  of  Azoic  rocks, 
lying  above  the  Primeval,  are  sedimentary  to  some  extent : 
they  are  not  all  completely  metamoiphic:  yet  they  are 
all  destitute  of  fossils.  This  is  the  fourth  and  last  difficulty 

*  F  f 


434          Darwin,  and  after  Darwin. 

which  has  to  be  met,  and  it  can  only  be  met  by  the  con- 
siderations which  have  been  advanced  by  Lyell  and  Darwin. 
The  former  says : — 

The  total  absence  of  any  trace  of  fossils  has  inclined  many 
geologists  to  attribute  the  origin  of  the  most  ancient  strata  to 
an  azoic  period,  or  one  antecedent  to  the  existence  of  organic 
beings.  Admitting,  they  say,  the  obliteration,  in  some  cases,  of 
fossils  by  plutonic  action,  we  might  still  expect  that  traces  of 
them  would  oftener  be  found  in  certain  ancient  systems  of  slate, 
which  can  scarcely  be  said  to  have  assumed  a  crystalline  structure. 
But  in  urging  this  argument  it  seems  to  be  forgotten  that  there 
are  stratified  formations  of  enormous  thickness,  and  of  various 
ages,  some  of  them  even  of  tertiary  date,  and  which  we  know 
were  formed  after  the  earth  had  become  the  abode  of  living 
creatures,  which  are,  nevertheless,  in  some  districts,  entirely 
destitute  of  all  vestiges  of  organic  bodies  '. 

He  then  proceeds  to  mention  sundry  causes  (in  addition  to 
plutonic  action)  which  are  adequate  to  destroy  the  fossiliferous 
contents  of  stratified  rocks,  and  to  show  that  these  may  well 
have  produced  enormous  destruction  of  organic  remains  in 
these  oldest  of  known  formations. 

Darwin's  view  is  that,  during  the  vast  ages  of  time 
now  under  consideration,  it  is  probable  that  the  distribution 
of  sea  and  land  over  the  earth's  surface  has  not  been  uni- 
formly the  same,  even  as  regards  oceans  and  continents. 
Now,  if  this  were  the  case,  "  it  might  well  happen  that  strata 
which  had  subsided  some  miles  nearer  to  the  centre  of  the 
earth,  and  which  had  been  pressed  on  by  an  enormous 
weight  of  superincumbent  water,  might  have  undergone  far 
more  metamorphic  action  than  strata  which  have  always 
remained  nearer  to  the  surface.  The  immense  areas  in 
some  parts  of  the  world,  for  instance  in  South  America, 
of  naked  metamorphic  rocks,  which  must  have  been  heated 
under  great  pressure,  have  always  seemed  to  me  to  require 

1  Elements  of  Geology,  p.  587. 


Appendix  to  Chapter  V.  435 

some  special  explanation ;  and  we  may  perhaps  believe  that  we 
see,  in  these  large  areas,  the  many  formations  long  anterior  to 
the  Cambrian  epoch  in  a  completely  metamorphosed  and 
denuded  condition1."  The  probability  of  this  view  he 
sustains  by  certain  general  considerations,  as  well  as  par- 
ticular facts  touching  the  geology  of  oceanic  islands,  &c. 

On  the  whole,  then,  it  seems  to  me  but  reasonable  to 
conclude,  with  regard  to  all  four  objections  in  question,  as 
Darwin  concludes  with  regard  to  them : — 

For  my  part,  following  out  Lyell's  metaphor,  I  look  at  the 
geological  record  as  a  history  of  the  world  imperfectly  kept, 
written  in  a  changing  dialect ;  of  this  history  we  possess  the  last 
volume  alone,  relating  only  to  two  or  three  countries.  Of  this 
volume,  only  here  and  there  a  short  chapter  has  been  preserved ; 
and  of  each  page  only  here  and  there  a  few  lines.  Each  word  of 
the  slowly-changing  language,  more  or  less  different  in  the 
successive  chapters,  may  represent  the  forms  of  life,  which 
are  entombed  in  our  consecutive  formations,  and  which  falsely 
appear  to  us  to  have  been  abruptly  introduced.  On  this  view, 
the  difficulties  above  discussed  are  greatly  diminished,  or  even 
disappear  *. 

As  far  as  I  can  see,  the  only  reasonable  exception  that 
can  be  taken  to  this  general  view  of  the  whole  matter,  is  one 
which  has  been  taken  from  the  side  of  astronomical 
physics. 

Put  briefly,  it  is  alleged  by  one  of  the  highest  authorities 
in  this  branch  of  science,  that  there  cannot  have  been  any 
such  enormous  reaches  of  unrecorded  time  as  would  be 
implied  by  the  supposition  of  there  having  been  a  lost  history 
of  organic  evolution  before  the  Cambrian  period.  The 
grounds  of  this  allegation  I  am  not  qualified  to  examine ; 
but  in  a  general  way  I  agree  with  Prof.  Huxley  in  feeling 
that,  from  the  very  nature  of  the  case,  they  are  necessarily 

1  Origin  of  Species,  p.  289. 
•  Ibid. 

F   f  2 


436          Darwin,  and  after  Darwin. 

precarious, — and  this  in  so  high  a  degree  that  any  conclusions 
raised  on  such  premises  are  not  entitled  to  be  deemed  for- 
midable \ 

Turning  now  to  plants,  the  principal  and  the  ablest 
opponent  of  the  theory  of  evolution  is  here  unquestionably 
Mr.  Carruthei  s 2.  The  difficulties  which  he  adduces  may  be 
classified  under  three  heads,  as  follows : — 

i.  There  is  no  evidence  of  change  in  specific  forms  of 
existing  plants.  Not  only  are  the  numerous  species  of 
plants  which  have  been  found  in  Egyptian  mummies  in- 
distinguishable from  their  successors  of  to-day ;  but,  what 
is  of  far  more  importance,  a  large  number  of  our  own 
indigenous  plants  grew  in  Great  Britain  during  the  glacial 
period  (including  under  this  term  the  warm  periods  between 
those  of  successive  glaciations),  and  in  no  one  case  does  it 
appear  that  any  modification  of  specific  type  has  occurred. 
This  fact  is  particularly  remarkable  as  regards  leaves, 
because  on  the  one  hand  they  are  the  organs  of  plants  which 
are  most  prone  to  vary,  while  on  the  other  hand  they  are 
likewise  the  organs  which  lend  themselves  most  perfectly 
to  the  process  of  fossilization,  so  that  all  details  of  their 
structure  can  be  minutely  observed  in  the  fossil  state.  Yet 
the  interval  since  the  glacial  period,  although  not  a  long  one 
geologically  speaking,  is  certainly  what  may  be  called  an 
appreciable  portion  of  time  in  the  history  of  Dicotyledonous 
plants  since  their  first  appearance  in  the  Cretaceous  epoch. 
Again,  if  we  extend  this  kind  of  enquiry  so  as  to  include  the 
world  as  a  whole,  a  number  of  other  species  of  plants  dating 
from  the  glacial  epoch  are  found  to  tell  the  same  story — 
notwithstanding  that,  in  the  opinion  of  Mr.  Carrulhers,  they 
must  all  have  undergone  many  changes  of  environment 

1  See  Lay  Sermons,  Lecture  on  Geological  Reform. 

2  See  especially  the  following  Presidential  addresses :  -  Gcol.  Assoc. 
Nov.  1876;  Section  D.  Brit.  Assoc.,  1886;  Lin.  Soc.,  1890. 


Appendix  to  Chapter  V.  437 

while  advancing  before,  and  retreating  after,  successive 
glaciations  in  different  parts  of  the  globe.  Or,  to  quote  his 
own  words  :— "  The  various  physical  conditions  which  of 
necessity  affected  these  [41]  species  in  their  diffusion  over 
such  large  areas  of  the  earth's  surface  in  the  course  of,  say, 
250,000  years,  should  have  led  to  the  production  of  many 
varieties ;  but  the  uniform  testimony  of  the  remains  of  this 
considerable  pre-glacial  flora,  as  far  as  the  materials  admit 
of  a  comparison,  is  that  no  appreciable  change  has  taken 
place." 

2.  There  is  no  appearance  of  generalized  forms  among 
the  earliest  plants  with  which  we  are  acquainted.     For  ex- 
ample, in  the  first  dry  land  flora — the  Devonian — we  have 
representatives  of  the  Fih'ces,  Equisetacea,  and  Lycopodz'acece, 
all  as  highly  specialized  as  their  living  representatives,  and 
exhibiting  the  differential  characters  of  these  closely  related 
groups.     Moreover,   these   plants   were   even  more   highly 
organized  than  their  existing  descendants  in  regard  to  their 
vegetative  structure,  and  in  some  cases  also  in  regard  to 
their  reproductive  organs.     So   likewise   the  Gymnosperms 
of  that  time  show  in  their  fossil  state  the  same  highly  organ- 
ized woody  structure  as  their  living  representatives. 

3.  Similarly,  and  more  generally,  the  Dicotyledonous  plants, 
which  first  appear  in  the  Cretaceous  rocks,  appear  there 
suddenly,  without  any  forms  leading  up  to  them — notwith- 
standing that  "  we  know  very  well  the  extensive  flora  of  the 
underlying  Wealden."    Moreover,  we  have  all  the  three  great 
divisions  of  the  Dicotyledons  appearing   together,  and   so 
highly  differentiated  that  all  the  species  are  referred  to  ex- 
isting genera,  with  the  exception  of  a  very  few  imperfectly 
preserved,  and  therefore  uncertain  fragments. 

Such  being  the  facts,  we  may  begin  by  noticing  that,  even 
at  first  sight,  they  present  different  degrees  of  difficulty. 
Thus,  I  cannot  see  that  there  is  much  difficulty  with 
regard  to  those  in  class  2.  Only  if  we  were  to  take  the 


438         Darwin,  and  after  Darwin. 

popular  (and  very  erroneous)  view  of  organic  evolution  as 
a  process  which  is  always  and  everywhere  bound  to  promote 
the  specialization  of  organic  types— only  then  ought  we  to 
see  any  real  difficulty  in  the  absence  of  generalized  types 
preceding  these  existing  types.  Of  course  we  may  wonder 
why  still  lower  down  in  the  geological  series  we  do  not 
meet  with  more  generalized  (or  ancestral)  types;  but  this 
is  the  difficulty  number  3,  which  we  now  proceed  to 
examine. 

Concerning  the  other  two  difficulties,  then,  the  only  possible 
way  of  meeting  that  as  to  the  absence  of  any  parent  forms 
lower  down  in  the  geological  series  is  by  falling  back — as  in 
the  analogous  case  of  animals — upon  the  imperfection  of  the 
geological  record.  Although  it  is  certainly  remarkable  that 
we  should  not  encounter  any  forms  serving  to  connect  the 
Dicotyledonous  plants  of  the  Chalk  with  the  lower  forms  of 
the  underlying  Wealden,  we  must  again  remember  that  diffi- 
culties thus  depending  on  the  absence  of  any  corroborative 
record,  are  by  no  means  equivalent  to  what  would  have 
arisen  in  the  presence  of  an  adverse  record — such,  for  in- 
stance, as  would  have  been  exhibited  had  the  floras  of  the 
Wealden  and  the  Chalk  been  inverted.  But,  as  the  case 
actually  stands,  the  mere  fact  that  Dicotyledonous  plants, 
where  they  first  occur,  are  found  to  have  been  already  differ- 
entiated into  their  three  main  divisions,  is  in  itself  sufficient 
evidence,  on  the  general  theory  of  evolution,  that  there  must 
be  a  break  in  the  record  as  hitherto  known  between  the 
Wealden  and  the  Chalk.  Nor  is  it  easy  to  see  how  the  op- 
ponents of  this  theory  can  prove  their  negative  by  furnishing 
evidence  to  the  contrary.  And  although  such  might  justly  be 
deemed  an  unfair  way  of  putting  the  matter,  were  this  the  only 
case  where  the  geological  record  is  in  evidence,  it  is  not  so 
when  we  remember  that  there  are  numberless  other  cases 
where  the  geological  record  does  testify  to  connecting  links  in 
a  most  satisfactory  manner.  For  in  view  of  this  consideration 


Appendix  to  Chapter   V.  439 

the  burden  of  proof  is  thrown  upon  those  who  point  to  par- 
ticular cases  where  there  is  thus  a  conspicuous  absence  of 
transitional  forms — the  burden,  namely,  of  proving  that  such 
cases  are  not  due  merely  to  a  break  in  the  record.  Besides, 
the  break  in  the  record  as  regards  this  particular  case  may 
be  apparent  rather  than  real.  For  I  suppose  there  is  no 
greater  authority  on  the  pure  geology  of  the  subject  than 
Sir  Charles  Lyell,  and  this  is  what  he  says  of  the  particular 
case  in  question.  "  If  the  passage  seem  at  present  to  be 
somewhat  sudden  from  the  flora  of  the  Lower  or  Neocomian 
to  that  of  the  Upper  Cretaceous  period,  the  abruptness  of 
the  change  will  probably  disappear  when  we  are  better  ac- 
quainted with  the  fossil  vegetation  of  the  uppermost  tracts  of 
the  Neocomian  and  that  of  the  lowest  strata  of  the  Gault,  or 
true  Cretaceous  series  V 

Lastly,  the  fact  of  the  flora  of  the  glacial  epoch  not 
having  exhibited  any  modifications  during  the  long  residence 
of  some  of  its  specific  types  in  Great  Britain  and  else- 
where, is  a  fact  of  some  importance  to  the  general  theory  of 
evolution,  since  it  shows  a  higher  degree  of  stability  on  the 
part  of  these  specific  types  than  might  perhaps  have  been  ex- 
pected, supposing  the  theory  to  be  true.  But  I  do  not  see  that 
this  cons:itutes  a  difficulty  against  the  theory,  when  we  have  so 
many  other  cases  of  proved  transmutation  to  set  against  it. 
For  instance,  not  to  go  further  afield  than  this  very  glacial 
flora  itself,  it  will  be  remembered  that  in  an  earlier  chapter 
I  selected  it  as  furnishing  specially  cogent  proof  of  the 
transmutation  of  species.  What,  then,  is  the  explanation  of 
so  extraordinary  a  difference  between  Mr.  Carruthers'  views 
and  my  own  upon  this  point  ?  I  believe  the  explanation  to 
be  that  he  does  not  take  a  sufficiently  wide  survey  of  the 
facts. 

To  begin  with,  it  seems  to  me  that  he  exaggerates  the 
vicissitudes  to  which  the  species  of  plants  that  he  calls  into 
1  Elements  of  Geology,  p.  280 


44-O          Darwin,  and  after  Darwin. 

evidence  have  been  exposed  while  advancing  before,  and 
retreating  after,  the  ice.  Rather  do  I  agree  with  Darwin 
that  "  they  would  not  have  been  exposed  during  their  long 
migrations  to  any  great  diversity  of  temperature ;  and  as  they 
all  migrated  in  a  body  together,  their  mutual  relations  will 
not  have  been  much  disturbed;  hence,  in  accordance  with 
the  principles  indicated  in  this  volume,  these  forms  will  not 
have  been  liable  to  much  modification  \"  But,  be  this 
matter  of  opinion  as  it  may,  a  much  better  test  is  afforded 
by  those  numerous  cases  all  the  world  over,  where  arctic 
species  have  been  left  stranded  on  alpine  areas  by  the  retreat 
of  glaciation ;  because  here  there  is  no  room  for  differences 
of  opinion  as  to  a  "  change  of  environment "  having  taken 
place.  Not  to  speak  of  climatic  differences  between  arctic 
and  alpine  stations,  consider  merely  the  changes  which  must 
have  taken  place  in  the  relations  of  the  thus  isolated  species 
to  each  other,  as  well  as  to  those  of  all  the  foreign  plants, 
insects,  &c.,  with  which  they  have  long  been  thrown  into 
close  association.  If  in  such  cases  no  variation  or  transmu- 
tation had  taken  place  since  the  glacial  epoch,  then  indeed 
there  would  have  been  a  difficulty  of  some  magnitude.  But, 
by  parity  of  reasoning,  whatever  degree  of  difficulty  would 
have  been  thus  presented  is  not  merely  discharged,  but 
converted  into  at  least,  an  equal  degree  of  corroboration, 
when  it  is  found  that  under  such  circumstances,  in  whatever 
part  of  the  world  they  have  occurred,  some  considerable 
amount  of  variation  and  transmutation  has  always  taken 
place, — and  this  in  the  animals  as  well  as  in  the  plants. 
For  instance,  again  to  quote  Darwin,  "If  we  compare  the 
present  Alpine  plants  and  animals  of  the  several  great  Euro- 
pean mountain-ranges  one  with  another,  though  many  of 
the  species  remain  identically  the  same,  some  exist  as  varie- 
ties, some  as  doubtful  forms  or  sub-species,  and  some  as 
distinct  yet  closely  allied  species  representing  each  other  on 
1  Origin  of  Species,  p.  332. 


Appendix  to  Chapter  V.  441 

the  several  ranges  V  Lastly,  if  instead  of  considering  the 
case  of  alp'ne  floras,  we  take  the  much  larger  case  of  the 
Old  and  New  World  as  a  whole,  we  meet  with  much  larger 
proofs  of  the  same  general  facts.  For,  "  during  the  slowly 
decreasing  warmth  of  the  Pliocene  period,  as  soon  as  the 
species  in  common,  which  inhabited  the  New  and  Old 
Worlds,  migrated  south  of  the  Polar  Circle,  they  will  have 
been  completely  cut  off  from  each  other.  This  separation, 
as  far  as  the  more  temperate  productions  are  concerned, 
must  have  taken  place  long  ages  ago.  As  the  plants  and 
animals  migrated  southward,  they  will  have  become  mingled 
in  one  great  region  with  the  native  American  productions, 
and  would  have  had  to  compete  with  them;  and,  in  the 
other  great  region,  with  those  of  the  Old  World.  Conse- 
quently we  have  here  everything  favourable  for  much  modifi- 
cation,— for  far  more  modification  than  with  the  Alpine 
productions  left  isolated,  within  a  much  more  recent  period, 
on  the  several  mountain  ranges  and  on  the  arctic  lands  of 
Europe  and  N.  America.  Hence  it  has  come,  that  when 
we  compare  the  now  living  productions  of  the  temperate 
regions  of  the  New  and  Old  Worlds,  we  find  very  few  iden- 
tical species ;  but  we  find  in  every  class  many  forms,  which 
some  naturalists  rank  as  geographical  races,  and  others  as 
distinct  species ;  and  a  host  of  closely  allied  or  representative 
forms  which  are  ranked  by  all  naturalists  as  specifically 
distinct 2." 

In  view  then  of  all  the  above  considerations — and 
especially  those  quoted  from  Darwin— it  appears  to  me  that 
far  from  raising  any  difficulty  against  the  theory  of  evolution, 
the  facts  adduced  by  Mr.  Carruthers  make  in  favour  of  it. 
For  when  once  these  facts  are  taken  in  connection  with  the 
others  above  mentioned,  they  serve  to  complete  the  cor- 
respondence between  degrees  of  modification  with  degrees 

1  Origin  of  Species,  p.  332. 

*  Ibid.  pp.  333-4- 


442  Darwin,  and  after  Darwin. 

of  time  on  the  one  hand,  and  with  degrees  of  evolution,  of 
change  of  environment,  &c.,  on  the  other.  Or,  in  the 
words  of  Le  Conte,  when  dealing  with  this  very  subject,  "  It 
is  impossible  to  conceive  a  more  beautiful  illustration  of 
the  principles  we  have  been  trying  to  enforce  V 

1  Evolution  and  its  Relation  to  Religious  Thought,  p.  194. 


NOTE  A  TO  PAGE  257. 

The  passages  in  Dr.  Whewell's  writings,  to  which  allusion  is 
here  made,  are  somewhat  too  long  to  be  quoted  in  the  text.  But 
as  I  think  they  deserved  to  be  given,  I  will  here  reprint  a  letter 
which  I  wrote  to  Nature  in  March,  1888. 

In  his  essay  on  the  Reception  of  the  Origin  of  Species,  Prof.  Huxley 
writes  : — 

"  It  is  interesting  to  observe  that  the  possibility  of  a  fifth  alterna- 
tive, in  addition  to  the  four  he  has  stated,  has  not  dawned  upon  Dr. 
Whewell's  mind  "  (Life  and  Lectures  of  Charles  Darwin,  vol.  ii,  p. 
195)- 

And  again,  in  the  article  Science,  supplied  to  The  Reign  of  Queen 
Victoria,  he  says  : — 

"  Whewell  had  not  the  slightest  suspicion  of  Darwin's  main  theorem, 
even  as  a  logical  possibility  "  (p  365). 

Now,  although  it  is  true  that  no  indication  of  such  a  logical 
possibility  is  to  be  met  with  in  the  History  of  the  Inductive  Sciences, 
there  are  several  passages  in  the  Bridgewater  Treatise  which  show  a 
glimmering  idea  of  such  a  possibility.  Of  these  the  following  are, 
perhaps,  worth  quoting.  Speaking  of  the  adaptation  of  the  period  of 
flowering  to  the  length  of  a  year,  he  says  : — 

<;  Now  such  an  adjustment  must  surely  be  accepted  as  a  proof  of 
design,  exercised  in  the  formation  of  the  world.  Why  should  the 
solar  year  be  so  long  and  no  longer?  or,  this  being  such  a  length, 
why  should  the  vegetable  cycle  be  exactly  of  the  same  length  ?  Can 
this  be  chance  ?  .  .  . .  And,  if  not  by  chance,  how  otherwise  could 
such  a  coincidence  occur  than  by  an  intentional  adjustment  of  these 
two  things  to  one  another  ;  by  a  selection  of  such  an  organization  in 
plants  as  would  fit  them  to  the  earth  on  which  they  were  to  grow  ; 
by  an  adaptation  of  construction  to  conditions  ;  of  the  scale  of  con- 
struction to  the  scale  of  conditions?  It  cannot  be  accepted  as  an 
explanation  of  this  fact  in  the  economy  of  plants,  that  it  is  necessary 
to  their  existence;  that  no  plants  could  possibly  have  subsisted, 


444  Darwin,  and  after  Darwin. 

and  come  down  to  us,  except  those  which  were  thus  suited  to  their 
place  on  the  earth.  This  is  true  ;'but  it  does  not  at  all  remove  the 
necessity  of  recurring  to  design  as  the  origin  of  the  construction  by 
which  the  existence  and  continuance  of  plants  is  made  possible.  A 
watch  could  not  go  unless  there  were  the  most  exact  adjustment  in 
the  forms  and  positions  of  its  wheels ;  yet  no  one  would  accept  it  as 
an  explanation  of  the  origin  of  such  forms  and  positions  that  the  watch 
would  not  go  if  these  were  other  than  they  were.  If  the  objector  were 
to  suppose  that  plants  were  originally  fitted  to  years  of  various  lengths, 
and  that  such  only  have  survived  to  the  present  time  as  had  a  cycle 
of  a  length  equal  to  our  present  year,  or  one  which  could  be  accom- 
modated to  it,  we  should  reply  that  the  assumption  is  too  gratuitous 
and  extravagant  to  require  much  consideration." 

Again,  with  regard  to  "the  diurnal  period,"  he  adds: — 
"Any  supposition  that  the  astronomical  cycle  has  occasioned  the 
physiological  one,  that  the  structure  of  plants  has  been  brought  to  be 
what  it  is  by  the  action  of  external  causes,  or  that  such  plants  as 
could  not  accommodate  themselves  to  the  existing  day  have  perished, 
would  be  not  only  an  arbitrary  and  baseless  assumption,  but,  more- 
over, useless  for  the  purposes  of  explanation  which  it  professes,  as 
we  have  noticed  of  a  similar  supposition  with  respect  to  the  annual 
cycle." 

Of  course  these  passages  in  no  way  make  against  Mr.  Huxley's 
allusions  to  Dr.  Whewell's  writings  in  proof  that,  until  the  publi- 
cation of  the  Origin  of  Species,  the  "  main  theorem  "  of  this  work  had 
not  dawned  on  any  other  mind,  save  that  of  Mr.  Wallace.  But 
these  passages  show,  even  more  emphatically  than  total  silence  with 
regard  to  the  principle  of  survival  could  have  done,  the  real  distance 
which  at  that  time  separated  the  minds  of  thinking  men  from  all  that 
was  wrapped  up  in  this  principle.  For  they  show  that  Dr.  Whewell, 
even  after  he  had  obtained  a  glimpse  of  the  principle  "  as  a  logical 
possibility,"  only  saw  in  it  an  "  arbitrary  and  baseless  assumption." 
Moreover,  the  passages  show  a  remarkable  juxtaposition  of  the  very 
terms  in  which  the  theory  of  natural  selection  was  afterwards  for- 
mulated. Indeed,  if  we  strike  out  the  one  word  "intentional" 
(which  conveys  the  preconceived  idea  of  the  writer,  and  thus 
prevented  him  from  doing  justice  to  any  naturalistic  view),  all  the 
following  parts  of  the  above  quotations  might  be  supposed  to  have 
been  written  by  a  Darwinian.  "  If  not  by  chance,  how  otherwise 
could  such  a  coincidence  occur,  than  by  an  adjustment  of  these  two 
things  to  one  another ;  by  a  selection  of  such  an  organization  in 
plants  as  would  fit  them  to  the  earth  on  which  they  were  to  grow  ; 
by  an  adaptation  of  construction  to  conditions ;  of  the  scale  of  con- 
struction to  the  scale  of  conditions  ?  "  Yet  he  immediately  goes  on  to 


Note  B  to  Page  295.  445 

say  :  "  If  the  objector  were  to  suppose  that  plants  were  originally 
fitted  to  years  of  various  lengths,  and  that  such  only  have  survived  to 
the  present  time  .  .  .  as  could  be  accommodated  to  it  (i.  e.  the 
actual  cycle),  we  should  reply  that  the  assumption  is  too  gratuitous 
and  extravagant  to  require  much  consideration."  Was  there  ever  a 
more  curious  exhibition  of  failure  to  perceive  the  importance  of  a 
"logical  possibility  "  ?  And  this  at  the  very  time  when  another  mind 
was  bestowing  twenty  years  of  labour  on  its  "  consideration." 


NOTE  B  TO  PAGE  295. 

Since  these  remarks  were  delivered  in  my  lectures  as  here 
printed,  Mr.  Mivart  has  alluded  to  the  subject  in  the  following 
and  precisely  opposite  sense  : — 

Many  of  the  more  noteworthy  instincts  lead  us  from  manifesta- 
tions of  purpose  directed  to  the  maintenance  of  the  individual,  to  no 
less  plain  manifestations  of  a  purpose  directed  to  the  preservation  of 
the  race.  But  a  careful  study  of  the  interrelations  and  interdepen- 
dencies  which  exist  between  the  various  orders  of  creatures  inhabiting 
this  planet  shows  us  yet  a  more  noteworthy  teleology—  the  existence 
of  whole  orders  of  such  creatures  being  directed  to  the  service  of 
other  orders  in  various  degrees  of  subordination  and  augmentation 
respectively.  This  study  reveals  to  us,  as  a  fact,  the  enchainment  of 
all  the  various  orders  of  creatures  in  a  hierarchy  of  activities,  in 
harmony  with  what  we  might  expect  to  find  in  a  world  the  outcome 
of  a  First  Cause  possessed  of  intelligence  and  will '. 

Having  read  this  much,  a  Darwinian  is  naturally  led  to  expect 
that  Mr.  Mivart  is  about  to  offer  some  examples  of  instincts 
or  structures  exemplifying  what  in  the  margin  he  calls  the 
"  Hierarchy  of  Ministrations."  Yet  the  only  facts  he  proceeds 
to  adduce  are  the  sufficiently  obvious  facts,  that  the  inorganic 
world  existed  before  the  organic,  plants  before  herbivorous 
animals,  these  before  carnivorous,  and  so  on  :  that  is  to  say, 
everywhere  the  conditions  to  the  occurrence  of  any  given  stage 
of  evolution  preceded  such  occurrence,  as  it  is  obvious  that  they 
must,  if,  as  of  course  it  is  not  denied,  the  possibility  of  such 
occurrence  depended  on  the  precedence  of  such  conditions. 
1  On  Truth,  p.  493. 


446          Darwin,  and  after  Darwin. 

Now,  it  is  surely  obvious  that  such  a  "  hierarchy  of  ministrations" 
as  this,  far  from  telling  against  the  theory  of  natural  selection,  is 
the  very  thing  which  tells  most  in  its  favour.  The  fact  that 
animals,  for  instance,  only  appeared  upon  the  earth  after  there 
were  plants  for  them  to  feed  upon,  is  clearly  a  necessity  of  the 
case,  whether  or  not  there  was  any  design  in  the  matter.  Such 
"  ministrations,"  therefore,  as  plant-organisms  yield  to  animal- 
organisms  is  just  the  kind  of  ministration  that  the  theory  of 
natural  selection  requires.  Thus  far,  then,  both  the  theories — 
natural  selection  and  super-natural  design — have  an  equal  right 
to  appropriate  the  facts.  But  now,  if  in  no  one  instance  can 
it  be  shown  that  the  ministration  of  plant-life  to  animal-life  is 
of  such  a  kind  as  to  subserve  the  interests  of  animal-life  without 
at  the  same  time  subserving  those  of  the  plant-life  itself,  then 
the  fact  makes  wholly  in  favour  of  the  naturalistic  explanation 
of  such  ministration  as  appears.  If  any  plants  had  presented 
any  characters  pointing  prospectively  to  needs  of  animals  without 
primarily  ministering  to  their  own,  then,  indeed,  there  would 
have  been  no  room  for  the  theory  of  natural  selection.  But  as 
this  can  nowhere  be  alleged,  the  theory  of  natural  selection  finds 
all  the  facts  to  be  exactly  as  it  requires  them  to  be  :  such  minis- 
tration as  plants  yield  to  animals  becomes  so  much  evidence 
of  natural  selection  having  slowly  formed  the  animals  to  appro- 
priate the  nutrition  which  the  plants  had  previously  gathered — 
and  gathered  under  the  previous  influence  of  natural  selection 
acting  on  themselves  entirely  for  their  own  sakes.  Therefore 
I  say  it  is  painfully  manifest  that  "  the  enchainment  of  all  the 
various  orders  of  creatures  in  a  hierarchy  of  activities,"  is 
not  "in  harmony  with  what  we  might  expect  to  find  in  a 
world  the  outcome  of  a  First  Cause  possessed  of  intelligence 
and  [beneficent]  will."  So  far  as  any  argument  from  such  "en- 
chainment" reaches,  it  makes  entirely  against  the  view  which 
Mr.  Mivart  is  advocating.  In  point  of  fact,  there  is  a  total 
absence  of  any  such  "  ministration  "  by  one  "  order  of  crea- 
tures" to  the  needs  of  any  other  order,  as  the  beneficent  design 
theory  would  necessarily  expect ;  while  such  ministration  as 
actually  does  obtain  is  exactly  and  universally  the  kind  which 
the  naturalistic  theory  requires. 

Again,  quite  independently,  and  still  more  recently,  Mr.  Mivart 


Note  B  to  Page  295.  447 

alluded  in  Nature  (vol.  xli,  p.  41)  to  the  difficulty  which  the 
apparently  exceptional  case  of  gall-formation  presents  to  the 
theory  of  natural  selection.  Therefore  I  supplied  (vol.  xli,  p.  80) 
the  suggestion  given  in  the  text,  viz.  that  although  it  appears  im- 
possible that  the  sometimes  remarkably  elaborate  and  adaptive 
structures  of  galls  can  be  due  to  natural  selection  acting  directly 
on  the  plants  themselves— seeing  that  the  adaptation  has  refer- 
ence to  the  needs  of  their  parasites — it  is  quite  possible  that 
the  phenomena  may  be  due  to  natural  selection  acting  indirectly 
on  the  plants,  by  always  preserving  those  individual  insects  (and 
larvae)  the  character  of  whose  secretions  is  such  as  will  best  in- 
duce the  particular  shapes  of  galls  that  are  required.  Several 
other  correspondents  took  part  in  the  discussion,  and  most  of 
them  accepted  the  above  explanation.  Mr.  T.  D.  A.  Cockerell, 
however,  advanced  another  and  very  ingenious  hypothesis, 
showing  that  there  is  certainly  one  conceivable  way  in  which 
natural  selection  might  have  produced  all  the  phenomena  of 
gall-formation  by  acting  directly  on  the  plants  themselves1. 
Subsequently  Mr.  Cockerell  published  another  paper  upon  the 
subject,  stating  his  views  at  greater  length.  The  following  is  the 
substance  of  his  theory  as  there  presented  : — 

Doubtless  there  were  internal  plant-feeding  larvae  before  there 
were  galls :  and,  indeed,  we  have  geological  evidence  that  boring  in- 
sects date  very  far  back  indeed.  The  primitive  internal  feeders,  then, 
were  miners  in  the  roots,  stems,  twigs,  or  leaves,  such  as  occur  very 
commonly  at  the  present  day.  These  miners  are  excessively  harmful 
to  plant-life,  and  form  a  class  of  the  most  destructive  insect-pests 
known  to  the  farmer :  they  frequently  cause  the  death  of  the  whole 
or  part  of  the  plant  attacked.  Now,  we  may  suppose  that  the  secre- 
tions of  certain  of  these  insects  caused  a  swelling  to  appear  where 
the  larvae  lived,  and  on  this  excrescence  the  larvae  fed.  It  is  easy  to 
see  that  the  greater  the  excrescence,  and  the  greater  the  tendency  ol 
the  larvae  to  feed  upon  it,  instead  of  destroying  the  vital  tissues,  the 
smaller  is  the  amount  of  harm  to  the  plant.  Now  the  continued  life 
and  vitality  of  the  plant  is  beneficial  to  the  larvae,  and  the  larger  or 
more  perfect  the  gall,  the  greater  the  amount  of  available  food. 
Hence  natural  selection  will  have  preserved  and  accumulated  the 
gall-forming  tendencies,  as  not  only  beneficial  to  the  larvae,  but  as  a 
means  whereby  the  larvae  can  feed  with  least  harm  to  the  plant.  So 

1  Nature,  vol.  xli,  p.  344. 


448  Darwin,  and  after  Darwin. 

far  from  being  developed  for  the  exclusive  benefit  of  the  larvae,  it  is 
easy  to  see  that,  allowing  a  tendency  to  gall-formation,  natural 
selection  would  have  developed  galls  exclusively  for  the  benefit  of  the 
plants,  so  that  they  might  suffer  a  minimum  of  harm  from  the  unavoid- 
able attacks  of  insects. 

But  here  it  may  be  questioned — have  we  proof  that  internal  feeders 
tend  to  form  galls  ?  In  answer  to  this  I  would  point  out  that  gall- 
formation  is  a  peculiar  feature,  and  cannot  be  expected  to  arise  in 
every  group  of  internal  feeders.  But  I  think  we  can  afford  sufficient 
proof  that  wherever  it  has  arisen  it  has  been  preserved  :  and  further, 
that  even  the  highly  complex  forms  of  galls  are  evolved  from  forms 
so  simple  that  we  hesitate  to  call  them  galls  at  all l. 

The  paper  then  proceeds  to  give  a  number  of  individual  cases. 
No  doubt  the  principal  objection  to  which  Mr.  Cockerell's 
hypothesis  is  open  is  one  that  was  pointed  out  by  Herr  Wet- 
terhan,  viz.  "  the  much  greater  facility  afforded  to  the  indirect 
action  through  insects,  by  the  enormously  more  rapid  succession 
of  generations  with  the  latter  than  with  many  of  their  vegetable 
hosts  — oaks  above  all2."  This  difficulty,  however,  Mr.  Cockerell 
believes  may  be  surmounted  by  the  consideration  that  a  growing 
plant  need  not  be  regarded  as  a  single  individual,  but  rather 
as  an  assemblage  of  such  ''. 


NOTE  C  TO  PAGE  394. 

The  only  remarks  that  Mr.  Wallace  has  to  offer  on  the 
pattern  of  colours,  as  distinguished  from  a  mere  brilliancy  of 
colour,  are  added  as  an  afterthought  suggested  to  him  by  the 
late  Mr.  Alfred  Tylor's  book  on  Colouration  of  Animals  and 
Plants  (1886).  But,  in  the  first  place,  it  appears  to  me  that 
Mr.  Wallace  has  formed  an  altogether  extravagant  estimate  of  the 
value  of  this  work.  For  the  object  of  the  work  is  to  show, 
"that  diversified  colouration  follows  the  chief  lines  of  structure, 
and  changes  at  points,  such  as  the  joints,  where  function 
changes."  Now,  in  publishing  this  generalization,  Mr.  Tylor— 
who  was  not  a  naturalist — took  only  a  very  limited  view  of  the 

1  Entomologist,  March,  1890.  2  Nature,  vol.  xli,  p.  394. 

3  Ibid.  vol.  xli,  pp.  559-560. 


Note  C  to  Page  394.  449 

facts.  When  applied  to  the  animal  kingdom  as  a  whole,  the 
theory  is  worthless;  and  even  within  the  limits  of  mammals, 
birds,  and  insects— which  are  the  classes  to  which  Mr.  Tylor 
mainly  applies  it— there  are  vastly  more  facts  to  negative  than 
to  support  it.  This  may  be  at  once  made  apparent  by  the 
following  brief  quotation  from  Prof.  Lloyd  Morgan  : — 

It  can  hardly  be  maintained  that  the  theory  affords  us  any  adequate 
explanation  of  the  specific  colour-tints  of  the  humming-birds,  or  the 
pheasants,  or  the  Papilionidae  among  butterflies.  If,  as  Mr.  Wallace 
argues,  the  immense  tufts  of  golden  plumage  in  the  bird  of  paradise 
owe  their  origin  to  the  fact  that  they  are  attached  just  above  the 
point  where  the  arteries  and  nerves  for  the  supply  of  the  pectoral 
muscles  leave  the  interior  of  the  body — and  the  physiological  rationale 
is  not  altogether  obvious, — are  there  no  other  birds  in  which  similar 
arteries  and  nerves  are  found  in  a  similar  position  ?  Why  have 
these  no  similar  tufts  ?  And  why,  in  the  birds  of  paradise  themselves, 
does  it  require  four  years  ere  these  nervous  and  arterial  influences 
take  effect  upon  the  plumage  ?  Finally,  one  would  inquire  how  the 
colour  is  determined  and  held  constant  in  each  species.  The  difficulty 
of  the  Tyloi  -Wallace  view,  even  as  a  matter  of  origin,  is  especially 
great  in  those  numerous  cases  in  which  the  colour  is  determined  by 
delicate  lines,  thin  plates,  or  thin  films  of  air  or  fluid.  Mr.  Poulton, 
who  takes  a  similar  line  of  argument  in  his  Colours  of  Animals 
(p.  326),  lays  special  stress  on  the  production  of  white  (pp.  201-202). 

As  regards  the  latter  point,  it  may  be  noticed  that  not  in  any 
part  of  his  writings,  so  far  as  I  can  find,  does  Mr.  Wallace  allude 
to  the  highly  important  fact  of  colours  in  animals  being  so 
largely  due  to  these  purely  physical  causes.  Everywhere  he 
argues  as  if  colours  were  universally  due  to  pigments ;  and  in 
my  opinion  this  unaccountable  oversight  is  the  gravest  defect 
in  Mr.  Wallace's  treatment  both  of  the  facts  and  the  philosophy 
of  colouration  in  the  animal  kingdom.  For  instance,  as  regards 
the  particular  case  of  sexual  colouration,  the  oversight  has  pre- 
vented him  from  perceiving  that  his  theory  of  *'  bril.iancy  "  as 
due  to  "a  surplus  of  vital  energy,"  is  not  so  much  as  logically 
possible  in  what  must  constitute  at  least  one  good  half  of  the 
facts  to  which  he  applies  it— unless  he  shows  that  there  is  some 
connection  between  vital  energy  and  the  development  of  stria- 
tions,  imprisonment  of  air-bubb'es,  &c.  But  any  such  connection 

*  G  g 


45°          Darwin,  and  after  Darwin. 

— so  essentially  important  for  his  theory — he  does  not  even 
attempt  to  show.  Lastly,  and  quite  apart  from  these  remarkable 
oversights,  even  if  Mr.  Tylor's  hypothesis  were  as  reasonable  and 
well-sustained  as  it  is  fanciful  and  inadequate,  still  it  could  not 
apply  to  sexual  colouration  :  it  could  apply  only  to  colouration 
as  affected  by  physiological  functions  common  to  both  sexes. 
Yet  it  is  in  order  to  furnish  a  "preferable  substitute"  for  Mr. 
Darwin's  theory  of  sexual  colouration,  that  Mr.  Wallace  adduces 
the  hypothesis  in  question  as  one  of  "  great  weight "  !  In  this 
matter,  therefore,  I  entirely  agree  with  Poulton  and  Lloyd 
Morgan. 


INDEX 


A. 

Accident,    Darwin's    use    of    the 

word,  334-340 ;  beauty  due  to, 

408,  409. 

Achromatin,  126-134. 
Acquired  characters, ^«  Characters. 
Acrcea  eurita,  328. 
Adaptation,    facts   of,  in   relation 

to   theory  of  natural  selection, 

401-403-  4". 

Adaptivecharncters,  .^Characters. 
Esthetic  sense  in   animals,   380- 

385  ;  see  Beautiful. 
Agassiz,  Prof.  A.,  on  fauna  of  the 

Mammoth  cave,  70. 
Alpine    plants,    209,    210,    440- 

442. 

Amauris  niavius,  328 
Amblyornis  inomata,  3^1   383. 
Amphiojctts,  137,  138,  145,  146. 
Analogy,    38,    50-65,    176,    177, 

347-35°- 

Anthropoid,  see  Apes. 

Antlers,  98-100,  167-169. 

Ants,  co-operative  instincts  of, 
268  ;  leaf-cutting,  332  ;  keeping 
aphides,  292. 

Ape,  eye  of,  75  ;  appendix  vermi- 
forinis  of,  84—86. 

Apes,  ears  of,  compared  with  those 
of  man,  88  ;  muscles  of,  77,  82, 
83;  feet  of,  77,  78;  tail  of, 
compared  with  that  of  man, 
82-84;  hair  of,  compared  with 
that  of  man,  89-91 ;  teeth  of, 
compared  with  those  of  man, 
92-94;  flattening  of  tibiae  of, 

95.  96- 
Aphides,  293. 

G 


Appendix  vermiformis  of  man 
c.  mpared  with  that  of  orang. 
84-86. 

Apteryx,  68,  69. 

Archizopteryx ,  171-173. 

Arctic  plants,  2:9,  210,  440-442. 

Argyll,  Dnke  of,  on  natural  selec- 
tion, 334-362. 

Aristotle,  his  idea  of  scientific 
method,  i ;  on  classification, 
23,  24. 

Arm,  distribution  of  hair  on,  in 
man  and  apes,  89-92. 

Arthropoda,  embryology  of,  155. 

Artificial  selection,  analogy  of, 
to  natural  selection,  295-314: 
pictorial  representations  of  pro  • 
ducts  of,  298-312. 

Artiodactyls,  182-191. 

Association,  piinciple  of,  in 
aesthetics,  404-407. 

Aster,  129-133. 

Attraction-spheres,  128,  132,  133. 

Australia,  fauna  of,  204,  20-. ; 
thriving  of  exotic  species  in, 
286 ;  portrait  of  wild  dog  of, 

3°4- 
Azores,  224,  225. 

B. 

Bacon,  Lord,  on  scientific  method, 2. 
Balanoglossus,  147,  148. 
Baptanodon  discus,  posteiior  limb 

of,  179-181. 
Barriers,  in  relation  to  geographical 

distribution,  216-224. 
Bats,  56,  224,  226,  240. 
Battle,  law  of,  385,  386. 
Baya-bird,  381. 


452 


Index. 


Bear,  skeleton  of,  174;  feet  of, 
178. 

Beautiful,  the,  sense  of,  in  animals, 
380-385 ;  standards  of,  380- 
404;  Darwin's  explanation  of, 
in  organic  nature,  379-411; 
facts  of,  in  inorganic  nature  in 
relation  to  Darwin's  theory  of, 
in  organic,  404 ;  often  determined 
by  natural  selection,  406,  407  ; 
absent  in  many  plants  and 
animals,  408 ;  in  nature  often 
accidental,  409-411  ;  does  not 
exist  in  organic  nature  as  an 
endorse,  410,  411. 

Bees,  co-operative  instincts  of, 
26*. 

Beetles,  wingless,  68-70 ;  on 
oceanic  islands,  224,  226,  229, 
232. 

Bell,  Dr.,  on  natural  theology,  412. 

Bell-bird,  396-398. 

Bembidium,  233. 

Bermudas,  225-227. 

Biology,  ideas  of  method  in,  1-9. 

Birds,  ovum  of,  1 24 ;  embryology 
of,  151-155;  palaeontology  of, 
163-165,  172,  173;  brain  of, 
194-197  ;  as  carriers  of  seed, 
eggs,  and  small  organisms,  217, 
218;  distribution  of,  224-240; 
aesthetic  sense  of,  380-385 ; 
courtship  of,  380-385. 

Birgus  latro,  62-65. 

Blood,  colour  of  aiterial,  409. 

Boar,  see  Pig. 

Bombus  lapidariits,  331. 

Bower-birds,  play-houses  of,  381- 

38.V 
Boyd-Dawkins,    on    flattening    of 

early  human  tibia-,  96. 
Brain,  palaeontology  of,  194-197. 
British  Isles,  sec  Islands. 
Broca,  363. 
Bronn,  363. 

Budding,  see  Germination. 
Burdon-Sanderson,Prof.,onelectric 

organ  of  skate,  366. 
Butler,  Bishop,  on  argument  from 

ignorance,  41. 
Butterflies,  defensive  colouring  of, 

321-329. 


Csesalpino,  on  classification,  24. 
Calf,  embryology  of,  153. 
Camel,  foot  of,  187-191. 
Canadian  stag,  196,  198,  199. 
Canaries,   portraits  of,   303 ;    first 

mentioned  by  Gesner,  312,  313. 
Cape    de    Verde    Archipelagoes, 

fauna  of,  2  >8. 

Carcharias  melancpterus,  1 49. 
Carruthers,  on  evolution,  436-442. 
Caterpillars,    colours    and    forms 

of,  319,  322-326. 
Cattle,  portraits  of,  311. 
Causation,  natural,  402,  413,  414. 
Caves,  faunas  of  dark,  70-72. 
Cell,  physiological,  and  properties 

of  the,  104-134. 
Centra  vinula,  325,  326. 
Cervalces  Americanus,  196,   198, 

199. 
Cervus    dicrocents,    issiodorensis, 

maiheronis,  panlinensis,  Sedg- 

"wickii,  tetraceros,  168. 
Chalmers,  Dr.,  on  natural  theology, 

412. 

Chameleons,  317. 
Characters,  as  adaptive,  273-276, 

286-293,  349 ;  as  specific,  274- 

276,    286-295;    as    congenital 

and  acquired,  274-276. 
Chasmorhynchus  niveus,  and  C. 

tricarunculalus,  396-3  8. 
Chelydra  serpentina,  anterior  limb 

of,  179-181. 

Chick,  embryology  of,  153. 
Chimpanzee,  see  Apes. 
Chlorophyll,  40^. 
C ' liondracanthus  cormitus,  122. 
Cirripedcs,  430. 
Classification,   23-49;    of  organic 

nature  by  Genesis  and  Leviticus, 

23 ;    artificial  and  natural,  24- 

26  ;   empirical  rules  of,  33-40  ; 

Darwin  on,  35,  36,  39,  40 ;  form 

of,    a   nexus    or    tree,    29  32 ; 

of  organic   forms   like  that  of 

languages,  32  ;  single  characters 

in  relation  to,  37  ;  aggregates  of 

characters  in  relation  to,  35-37  ; 

adaptive  and  non-adaptive  cha- 


Index. 


453 


racters  in  relation  to,  34,  35, 
38,  39 ;  chains  of  affinities  in 
relation  to,  39-40;  biological 
differs  from  astronomical,  43. 

Cockerell,  on  vegetable  galls, 
447,  448. 

Colours,  of  plants  and  animals  in 
relation  to  the  theory  of  natural 
selection,  317-332;  in  relation 
to  the  theory  of  sexual  selection, 

39'.    392,    394~39r>>    4°S-4IO> 

448-450. 
Colouring,  see  Recognition  marks, 

Protective,  Seasonal,  Warning, 

and  Mimicry. 
Congenital  characters,  see  Charac- 

teis. 
Conjugation,   of   Protozoa,    115- 

117. 
Continuity,  principle  of,  in  nature, 

15    21. 

Contrivance,  Darwin's  use  of  the 
word,  281. 

Co-operation,  mutual,  of  species 
alleged,  445-448. 

Co-operative  instincts,  due  to 
natural  selection,  267,  269. 

Cope,  Professor,  his  table  of  geo- 
logical formations,  163,  164; 
his  table  of  paloeontological 
development  of  feet,  vertebral 
column,  and  brain,  197. 

Correlation  of  growth,  357  3^2- 

Cossonida,  233. 

Courtship,  see  Sexual  Selection. 

Crabs,  62-65,  139. 

Cuttle-fish,  317. 

Cuvier,  on  method  in  natural 
history,  3-4  ;  on  monkeys,  429. 

Cyst,  see  Encystation. 

D. 

Darwin,  Charles,  his  influence  on 
ideas  of  method,  1-9;  on  classifi- 
cation, 35,  36,  39,  40 ;  on  ves- 
tigial characters  in  man,  77,  86, 
87,  92 ;  on  imperfection  of 
geological  record,  165,  and  Ap- 
pendix ;  on  means  of  dispersal, 
216,  218;  on  geogiapr.ical  dis- 
tribution, 218,  219;  on  fauna  of 


the  Galapagos  Archipelago,  227, 
228;  on  natural  selection,  252, 
253,  255,  256,  286,  375,  376; 
hisuseofbuchwordsas'acek'ent,' 
'  fortuitous,'  '  purpose,"  '  contri- 
vance,' &c.,  281,  334  340:  on 
sexual  selection,  379  400. 

Darwin,  Erasmus,  his  theory  of 
evolution,  253. 

De  Blainville,  on  the  theory  of 
descent,  258. 

De  Candolle,  on  classification,  34. 

Dter.  98,  99,  167-169,  187,  191, 
196,  i.,8,  199. 

Degeneration,  269,  270,  342. 

Delamination,  139. 

Dicuiema  euryla,  330. 

Diaster,  129-133. 

Dingo,  see  Dog. 

Dinornis,  60,  61. 

Diptera  mimicking  Hymenoptera, 
329. 

Dog,  dentition  of,  39 ;  Dingo,  304  ; 
domesticated  varieties  of,  305, 
307 ;  hairless,  307  ;  skulls  of, 

3°7- 

Duck,  logger-headed,  68. 
Dugong,  eye  of,  75. 

E. 

Eagle,  eye  of,  75. 

Ear,  of  whales,  65 ;  vestigial 
features  of  human,  76,  8^-89;  of 
man  and  apes  compared,  88. 

Eaton,  Rev.  A.  E.,  on  wingless 
insects,  70. 

Echinodcrmata,     125-127,      138, 

155- 

Ectoderm,  137-142. 

Kgg,  see  Ovum. 

Eimer,  363. 

Elaps  fttlvius  imitated  by  non- 
venomous  snakes,  330. 

Electric  organs,  365-373. 

Elephant,  foot  of,  185,  186;  rate 
of  propagation  of,  261,  262. 

Elk,  196-198,  199. 

Embryo,  human,  see  Man. 

Embryogeny,  see  Ontogeny. 

Embryology,  98-155. 

Embryos,  comparative  series  of, 
152,  153- 


454 


Index. 


Encyclopedia  Biilannlca,  eighth 
ed.,  on  instinct,  2*9-291. 

Encys'ation  of  Protozoa,   115. 

Kndoderm,  137-142. 

Equatorial  plate,  129. 

Equus,  see  Horse. 

Erytkrolanipi-us  vennstissimus, 
33°- 

Evolution,  organic,  fact  of,  Section 
I ;  Method  of,  Section  II ;  ideas 
upon,  prior  to  Darwin,  253-258; 
divergent,  266,  267. 

Ewart,  Professor  Cossar,  on  electric 
organ  of  skate,  364,  367. 

Existence,  see  Struggle  for. 

Eye,  of  octopus,  57,  58,  347-350; 
absence  of,  in  dark-cave  animals, 
70-72;  nictitating  membrane-  of, 
74>  75  5  development  of,  from 
cutaneous  nerve-ending,  352- 
354- 

F. 

Feet,  51-59,  66,  77-80,  174-192, 
K)7. 

Fertilization  of  ova,  127,  128  ;  of 
flowers  by  insects,  406. 

Fish,  embryology  of,  143-155; 
palaeontology  of,  163,  165,  169- 
171;  brain  of,  194- 197;  distribu- 
tion of,  224-246;  flying,  355. 

Fission,  reproduction  by,  106, 107. 

Flat  fish,  317. 

Float,  see  Swim-bladder. 

Flowers,  fertilization  of,  by  insects, 
406. 

Fly,  imitating  a  wasp,  329. 

Flying-fish,  and  squirrels,  355. 

Foraminifera,  346. 

Forbes,  H.  O.,  on  scapulo-coracoid 
bones  of  Dinornis,  60. 

Fortuitous,  Darwin's  use  of  the 
word,  340. 

Fossils,  see  Palaeontology. 

Frogs,  317. 

G. 

Galapagos  Islands,  227-231,  236, 

217. 

Galcus,  eye  of,  75. 
Galls,    vegetable,    293-295,    446- 

448. 


Gastraea,  137-140. 

Gastrophysema,  \  3S. 

(iastrulation,  137,  140. 

Gegenbaur,  147,  181. 

Gemmation,  reproduction  by,  106, 
107,  no,  in. 

Generalization,  5. 

Generalized  types,  33. 

Genesis,  classification  of  organic 
nature  in,  23. 

Genial  tubercle,  96. 

Geographical  distribution,  204- 
248:  see  Glacial  paiiod,  Barriers 
Transport  of  organisms,  Oceanic 
islands,  &c. 

Geology,  record  of  imperfect,  156- 
160,  and  Appendix  ;  see  Palae- 
ontology. 

Germs,  prophetic,  272,  351-362. 

Gesner,  on  classification,  24;  on 
canaries,  313. 

Gill-arches,  146,  147,  150,  151. 

Gill-slits,  146,  147,  150-153. 

Giiis,  of  young  salamanders,  102  ; 
origin  of,  in  embryo,  144 ;  of 
fish,  150,  152. 

Gi.affe,  neck  of,  in  relation  to 
Lamarck's  theory,  254. 

Glacial  periods,  effects  of,  on  dis- 
tribution of  plants  and  animals, 
209,  210,  and  Appendix 

Goose,  Frizzled,  portrait  of,  304. 

Gorilla,  see  Apes. 

Gray,  Professor  Asa,  337 

Great-toe,  in  man  and  apes,  79  81. 

Grouse,  317-319. 

Growth,  correlation  of,  357,  362. 

Gymnotus,  365,  367. 

H. 

Hack  el,  on  analogy  between 
species  and  languages,  32  ;  on 
reproduction  as  discontinuous 
growth,  105,  106;  his  ideal 
primitive  vertebrate,  143,  144. 

Hair,  vestigial  characters  of,  in 
man,  89  92. 

Hnles,  3. 

Haller,  3. 

Hamilton,  Sir  William,  273. 

Hands,  51-55,  66,  80-82,174-192. 

Hare,  318,  319. 


Index. 


455 


Hartmann,  on  flattening  of  early 
human  tibire,  96. 

Harvey,  on  Lord  Bacon's  writings, 
2. 

Heart,  development  of,  154. 

Heilprin,  on  skulls  of  deer,  198, 
199;  on  fossil  shells,  201,  202. 

Hen,  ovum  of,  122. 

Heredity,  in  relation  to  classifica- 
tion, 28-31  ;  in  relation  to  em- 
bryology, 98-102  ;  chromatin- 
fibres  in  relation  to,  134 ;  in 
relation  to  theories  of  organic 
evolution,  253-255,  250-264, 

377- 

Heimit-crabs,  62-65,  288,  289. 
Heteromera,  233 
Hilgendorf,  on  shells  of  Planorbis, 

201. 

Hipparion,  191,  192. 
Hippopotamus,  foot  of,  187. 
Hog,  see  Pig. 
Homology,  38,  50-65,  176,  177, 

347-35°,  3577359- 

Homopterons  insect,  imitating 
leaf-cutting  ants,  331.  332. 

Hooker,  Sir  Joseph,  on  flora  of 
St.  Helena,  234 

Horns,  98-100,  167-169. 

Horse,  eye  of,  75  ;  limb-bones  of, 
176,  177,  186,  188-192;  teeth 
of,  189-191;  portraits  of  do- 
mesticated breeds  of,  309. 

Human,  see  Man. 

Humerus,  perforations  of,  in  quad- 
rumana  and  man,  94,  95. 

Humming-birds,  restricted  to  the 
New  World,  an. 

Hunter,  3  ;  on  ear  of  whale,  65. 

Huxley,  Prof.,  on  mechanical  se- 
lection, 283;  on  age  of  the  earth, 
435. 436  5  on  Dr-  VYhewell,  243. 

Hyatt,  on  shells  of  Planorbis,  201. 

Hydra,  in,  122. 

Hyrax,  foot  of,  185,  186. 

I. 
Ignorance,  argument  from,  41,  42, 

49. 

Illative  Sense,  6. 
Imitative  colours,  317-323.   32°- 

332. 


Infant,  feet  of,  78,  79;  grasping 
power  of,  81. 

Infertility,  inter-specific,  in  relation 
to  natural  selection,  374-3,6. 

Insects,  wingless,  68-70;  in  pri- 
mary formations,  163,  Appendix ; 
on  oceanic  islands,  224-238;  in 
relation  to  galls,  293-295,  446- 
448;  defensive  colouring  of,  321- 
332 ;  fertilizing  flowers,  406. 

Instincts,  always  of  primary  use  to 
specitspresentingthem,286-2  ^3. 

Intercrossing,  in  relation  to  natural 
selection,  374-376. 

Inutility  of  specific  characters,  in 
relation  to  natural  selection, 
374-376. 

Islands,  oceanic,  224-237  ;  British, 
238-241. 

J- 

Japan,  hairless  dog  of,  IO1. 
Jelly-fish,  119,  no. 

K. 

Kallima,  323. 

Karyokinesis,   112-114,  128-134. 

Kepler,  272. 

Kerguelen  Island,  flightless  in- 
sects of,  70. 

Kropotkin,  Prince,  on  co-operative 
instincts,  269. 

L. 

Lagopus  mutus,  317,  318. 

Lamarck,  his  method  in  natural 
history,  4 ;  his  theory  of  evolu- 
tion, 253-256. 

Lamprey,  148. 

Languages,  classification  of,  re- 
sembles that  of  organic  forms. 

Lanke=ter,  E.  Ray,  on  karyo- 
kinesis,  129,  130. 

Leaf  insect,  322. 

Le  Conte,  on  geological  succession 
of  animal  classes,  164,  165;  on 
types  of  tails,  169-173;  on  fossil 
shells  of  Planoiliis,  201  ;  his 
work  on  the  relation  of  the 
theory  of  evolution  to  religious 
thought,  412. 


456 


Index. 


Leptalis,  328. 
Leuculmis  echinus,  122. 
Leviticus,  classification  of  organic 

nature  in,  23. 
Life,  origin  of,  15. 
Linnaeus,   on   method    in  natuial 

history,  3 ;  oil  classification,  26, 

3.5-4°- 

Lion,  skeleton  of,  175  ;  feet  of,  1 78. 

Lizard,  heart  and  gill-arches  of, 
150. 

Lloyd  Morgan,  273,  449,  450. 

Lungs,  development  of,  154,  354. 

Lyell,  Sir  Charles,  on  classification, 
32  ;  on  uniformitarianism,  258  ; 
on  rational  species,  344 ;  on  geo- 
logical record,  420,  435,  439. 

M. 

Madeira,  wingless  beetles  of,  68- 
70  ;  peculiar  beetles  of,  226,  227. 

Mammals,  ovum  of,  120-124;  em- 
bryology of,  151-155  jpalseonto- 
logy  of,  163,  165,  167,  i8o-/99; 
limbs  0^174-178,182-199;  brain 
of,  194-199;  of  Australia  and 
New  Zealand,  204,  205;  distri- 
bution of,  on  islands,  224-240. 

Mammoth  cave,  fauna  of,  70-72. 

Man,  nictitating  membrane  of,  7; ; 
vestigial  muscles  of,  J6,  77, 
82,  83 ;  tail  of,  compared  with 
that  of  apes,  82-84;  hair  o', 
compared  with  that  of  apes,  89- 
92 ;  teeth  of,  compared  with 
those  of  apes,  92-94 ;  perforati  :n 
of  humerus  of,  94,  95  ;  flattening 
of  ancient  tibiae  of,  95,  96 ; 
embryology  of,  119,  153;  hand 
of,  54 ;  arm  of,  90,  91  ;  limb- 
bones  of,  1 76, 1 77 ;  palaeontology 
of,  163,  165  ;  brain  of,  194,  195  ; 
Mr.  Syme  on,  346,  347. 

Marsh,  on  palaeontology  of  the 
horse,  188-190. 

Matthew,  Patrick,  on  natural 
selection,  257. 

Mesoclerm,  142. 

Mesohippus,  189,  192. 

Metaphyta,  104,  105. 

Metazoa,  104. 


Method,  ideasof,  in  natural  history, 
1-9  ;  of  organic  evolution,  252- 
261. 

Meyer,  Professor  Ludwig,  on  helix 
of  the  human  ear,  86. 

Mimicry,  320-322. 

Ministration,  mutual,  of  species 
alleged,  445,  446. 

Miohippus,  189. 

Mivart,  St.  George,  on  eye  of 
octopus,  57,  58,  348,  349;  on 
incipient  organs,  362  ;  on  mutual 
ministration  of  species,  445,  446. 

Mollusca,  shells  of,  19,  199-203; 
eye  of,  57,  58  ;  embryology  of, 
155  ;  palaeontology  of,  163,  165. 

Monkeys,  why  all,  do  not  become 
men,  342-344. 

Monotremata,  205. 

Morgan,  see  Lloyd  Morgan. 

Morphology,  50-97. 

Mule,  portrait  of,  309. 

Multicellular  organisms,  104. 

Multiplication,  see  Reproduction. 

N. 

Nageli,  Prof.,  337,  367. 

Natural  History,  ideas  of  method 
in,  1-9. 

Natural,  interpretations  as  opposed 
to  super-natural,  13-13  ;  causa- 
tion, 13-15. 

Natural  selection,  252-378,  401- 
410;  Wells,  Matthew,  and 
Whewell  on,  257,  258,443-445  ; 
statement  of  theory  of,  256-2X4, 
of  evidences  of,  285-332,  of 
criticisms  of,  333-378  ;  relation 
of  theory  of,  to  religiousthought, 
401-410;  preserves  types,  264- 
267  ;  cessation  and  reversal  of, 
270,  342 ;  errors  touching  theory 
of,  270-284,  332-364  ;  definition 
of.  275-376;  antecedent  standing 
of  theory  of,  277-284;  Prof. 
Owen  on,  333,  334;  Duke  of 
Argyll  on,  334-362  ;  Mr.  Syme 
on,  340,  341,  345  ;  need  not 
always  make  for  improvement, 
341-347  ;  homology  and  analogy 
in  relation  to,  347-350 ;  often 
determines  beauty,  406,  407;  in 


Index. 


457 


relation  totheformationofgalls, 

293-295,  446-448. 
Nature,  organic,  17;  inorganic,  I, 

17,  18. 

Nauplitu,  138. 
Neumayr,  19. 
New  Zealand,  fauna  of,  68,  204, 

205  ;  thriving  of  exotic  specits 

in,  286. 

Newman,  on  the  Illative  S'  use.  6. 
Newton,    his    idea    of     scier.t.fic 

method,  6. 

Nictitating  membrane,  74,  75. 
Notochord,  146. 
Novum  Organon,  the,  on  scientific 

method,  2. 

Nucleus,  105,  112-134. 
Nucleus-spindle,  129. 
Nut-hatch.     Syrian,     ornamented 

nests  of,  381. 

O. 

Objective  methods,  6. 
Oceanic  islands,  see  Islands. 
Octopus,  eye  of,  57,  58,  348-350. 
CEdicnenius  crepitans,  320. 
Ontogeny,    as    recapitulation     of 

phylogeny,  98-104. 
Oiang  Outang,  see  Apes. 
Oreilon  Culbertsoni,  167. 
Origin   of  Speci<  s,   the,   influence 

exercised  by,  on  ideas  of  method, 

19. 

Orohippus,  189. 
Otana  eye  of,  75. 
Ovum,  113-142;  human,  120-123; 

amoeboid  movements  of  young, 

121-123;  segmentation  of,  134, 

J35- 
Owen,  on  ear   of  whale,  65;    on 

natural  selection,  333,  334. 
Owl,  eye  of,  75. 

P. 

Paddle,  see  Whale,  and  Baptanodon 

discus. 

Pagunts  bernhardus,  64. 
Pain,  in  relation  to  the  theory  of 

evolution,  417. 
Palaeontology,    159-203;    gtneral 

testimony  of,  156-165;  te-timony 

of,  IP  particular  cases,  165-203  ; 


consideration  of  objections  to 
theory  of  evolution  founded  on 
grounds  of,  156-165,  and  Ap- 
pendix. 

Palteotherium,  190,191. 

Pnley,  on  natural  theology,  98,  412. 

Paludina,  successive  forms  of,  19. 

Panama,  Isthmus  of,  219. 

Panniculus  carnosjs,  77. 

Papilio  merope,  730. 

Parasites,  of  animals,  devoid  of 
beauty,  408. 

Parsimony,  law  of,  272. 

Parthenogenesis,  119. 

Parti  idges,  319. 

Peacock,  tail  of,  378  ;  courtship  of, 

383- 

Peck  ham,  Mr.  and  Mrs.,  on  court- 
ship of  spiders,  388-390. 
Perissodactyls,  182-192. 
Petromyzon  marinus,  148. 
Phenac odus  primtEVits,  184,  185. 
Phylogeny,  see  Ontogeny. 
Physiological  selection,  376. 
Pig,  embryology  of,  153  ;  feet  of, 

176,  187  ;   portraits  of  wild  and 

domesticated,  312. 
Pigeons,    portraits    of,  298,    299; 

leather-footed,  359. 
Pilot  fish,  289. 
Planorbis,  transmutations  of,  200, 

201. 
Pleasure  and  pain,  in  relation  to 

the  theory  of  evolution,  417. 
Plica  semiliinaris,  75. 
Pliohippus,  .89 
Polar  Lear,  skeleton  of,  174;  ttet 

of,  178. 

Polar  bodies,  125, 126. 
Polar  star,  129. 
Polyps,  114. 
Poi  poises,  24,  25,  50. 
Poulton,  E.  B.,  on  warning  colours, 

325,  326;  on  mimicry,  331,  332  ; 

sexual  selection,  400,  401,  449, 

450- 

Poultry,  portraits  of,  300-302. 
Pronucleus,  126-128. 
Prophetic  types,  272,  351-362. 
Prophysema  primordiale,  1 40. 
Protective  colouring,  317-323. 
Protohipfus,  189. 


Index. 


Protozoa,  104. 
Ptarmigan,  317,  318. 
Pterodactyl,  wing  of,  56. 
Purpose,  Darwin's  use  of  the  word, 

281,  340. 

Puss  moth,  larva  of,  325,  326. 
Python,  66,  67. 

Q. 

Quadrumana,  muscles  of,  76, 8  2,  83; 
perforations  of  humeri  of.  94, 
95  ;  hair  on  phalanges  of,  91. 

R. 

Rabbit,  embryology  of,  153  ;  mul- 
tiplication of,  in  Australia,  286  ; 
portraits  of  wild  and  domesticated 
breeds  of,  308 ;  protective  colour- 
ing of,  319,  320. 

Radiate  form,  beauty  of,  408,  409. 

Raia  radiata,  and  batis,  367  371. 

Rats,  species  of,  restricted  to  Old 
and  New  Worlds,  212;  British 
and  Norwegian,  285,  286. 

Rattle-snake,  tail  of,  289. 

Recognition  marks,  271-273. 

Religion,  in  relation  to  Darwinism, 
401-418. 

Reproduction,  different  methods  of, 
106-117  5  essence  of  sexual,  no; 
foreshadowing  of  sexual  in  uni- 
cellular organisms,  1 1 5-1 1 7. 

Reptiles,  wing  of  flying  56  ;  rudi- 
mentary limbs  of,  67;  nictitating 
membrane  of,  75 ;  branchial 
arches  of,  150;  embryology  of, 
152  ;  palaeontology  of,  163,  165, 
178-180;  brain  of,  194-197; 
distribution  of,  224-240. 

Rhinoceros,  foot  of,  186. 

Robinson,  Dr.  L.,  on  grasping 
power  of  an  infant'shands, 80-82. 

Rudimentary  organs,  65-97- 

Ruminants,  palaeontology  of,  167, 
168. 


Sacrum   of  man,  compared  with 

that  of  apes,  82-84. 
Sagitta,  138. 
Salamander,  young  of  terrestrial, 


living  in  water,  102;   embr)o 

logy  of,  152. 

Sandwich  Islands,  234-237. 
Science,  method  of,  1-9. 
Sclater,    W.  L.,    on    a    case    of 

mimicry,  331,  332. 
Scorpion   in   Silurian    formation, 

163. 
Sen,    lamprey,     148;    destructive 

agency  of  the,  423,  424. 
Seal,  51,  52,  75. 
Seasonal  changes  of  colour,  317- 

3!9. 

Selection,  value,  275  ;  by  physical 
processes,  282,  283,  335.  See 
also  Natural  selection,  Artificial 
selection,  Sexual  selection,  Phy- 
siological selection. 

Sentiency,  in  relation  to  the 
theory  of  evolution,  417. 

Sex,  difference  of,  restricted  to 
Metazoa  and  Metaphyta,  105. 

Sexual  reproduction,  see  Repro- 
duction. 

Sexual  selection,  theory  of,  277, 
378—410;  statement  and  evi- 
dences of,  379- '9 1  ;  criticisms 
of,  391-400;  includes  law  of 
battle  with  that  of  charming, 
385.  386;  in  relation  to  religious 
thought,4i  1-418 ;  Tylor's  theory 
substituted  for,  by  Wallace,  449, 

45°- 
Shark,   eye  of,    75  ;    man-eating 

149 ;  and  pilot-fish,  289. 
Sheep,  limb-bones  of,  176,    177; 

portraits  of,  310. 
Shells,  of  crabs,  62-64 ;  palaeon- 

tology  of  mollusk's,   199-203  ; 

land   on  oceanic  islands,   224- 

240. 
Silliman's  Journal,  on  fauna  of  the 

Mammoth  Cave,  70. 
Skate,  electric  organ  of,  364-373- 
Skull,  palaeontology  of,  io.4-]<;9; 

of  bull-dog  compared  with  that 

of  deer-hound,  307. 
Slavonia,    Tertiary    deposits    of, 

18,  19. 
Species,   not    eternal,   but   either 

created  or  evolved,  13  ;   named 

as    such    through    absence     of 


Index. 


459 


intermediate  forms,  18-20; 
groups  of,  in  classification,  20, 
and  appearing  suddenly  in 
geological  formations,  427-432, 
437-440;  origin  of,  coincide 
in  space  and  time  with  pre- 
existing and  allied  species, 
22  ;  geographical  distribution 
of,  204-248  ;  extinct  and  living 
allied  on  same  areas.  213;  life 
of,  preserved  by  natural  selec- 
tion, 264-270 ;  not  room  for 
more  than  one  rational,  344  ; 
characters  of,  274-276,  286— 
295»  374~~376  ;  inter-sterility  of 
allied,  374-376  ;  mutual  minis- 
tration of  alleged,  4/15,  446. 

Specific  characters,  see  Characters. 

Speculation,  method  of,  3-9. 

Spencer,  Herbert,  on  reproduction 
as  discontinuous  growth,  105, 
106 ;  on  use-inheritance,  253- 
256  ;  his  failure  to  conceive  the 
idea  of  natural  selection,  257. 

Spermatozoa,  123,  126-128. 

Spiders,  in  primary  formations, 
163  ;  courtship  of,  388,  389. 

Sponges,  122,  139,  140. 

Spontaneous,  Darwin's  use  of  the 
term,  340. 

Spores,  115. 

Squirrels,  flying,  355. 

Sterility,  see  Infeitility. 

St.  Helena,  231-234,  236-237. 

St.  Hilaire,  4. 

Stick-insect,  322. 

Stoat,  318. 

Strombus  accipitrinus,  2C " 

Strombus  Leiiiy  201. 

Struggle  for  existence,  259-270. 

Subjective,  methods,  6. 

Survival  of  the  fittest,  335.  See 
also  Natural  selection. 

Swim-bladder  of  fish,  154,  354. 

Symbiosis,  269. 

Syme,  David,  on  the  theory  of 
natural  selection,  340,  341. 

T. 
Tail,  types  of,  in  fish  and  birds, 

169-173. 
Tasmanian  wolf,  dentition  of,  39. 


Teeth,  of  Tasmaninn  wolf,  39  ; 
molar,  of  man,  compared  with 
those  of  apes,  92-94  ;  palaeon- 
tology of  horses',  189-191. 

Temperature,  sense  of,  probable 
origin  of  that  of  sight,  353.  354. 

Tennyson,  266. 

Tibiae,  flattening  of,  95,  96. 

Tissue-cells,  see  Cell. 

Toes,  79,  80 ;  see  also  Feet. 

Tomes,  C.  S.,  on  molar  teeth  of 
man  and  apes,  94. 

Torpedo,  365,  367. 

Tortoise,     embryology    of,     152, 

'54- 

Toxopneustes  variegatus,  and  T. 
lividus,  122. 

Transport  of  organisms,  means  of, 
207,  216-218. 

Tribal  fitness,  as  distinguished 
from  individual,  267-269. 

Trout,  ovum  of,  122. 

Turtle,  eye  of,  75. 

Tylor,  Alfred,  on  colouration  of 
animals,  448-450. 

Type,  preserved  by  natural  selec- 
tion, 264-269;  improvement  of, 
by  natural  selection,  269,  270; 
prophetic,  272,  351-362. 

Types,  as  simple  and  generalized, 

u. 

Unicellular  organisms,  104. 

[/raster,  138. 

Utility,  of  specific  characters,  774, 
275 ;  of  incipient  characters, 
351-363;  of  electric  organs, 
*•>  373-  y 

•  Variation,  in  relation  to  natural 
selection,  263,  335-34°.  377- 

Verification,  6-9. 

Veitebral  column,  embryology  of 
145,  146 ;  palaeontology  of, 
192,  193. 

Vertebrated  animal,  ideal  primi- 
tive, 143,  144;  embryology  of, 

143- "55- 

Vespa  vulgaris,  331. 
Vestigial  organs,  65-97. 
Volucella   inans,   and   V.  bomby- 

lans,  329. 


Index. 


Wagner,  Moritz,  on  geographical 
distribution,  216. 

Wallace,  A.  K.,  on  origin  of 
species  as  coincident  in  time 
and  space  with  pre-existing  and 
allied  species,  22  ;  on  wingless 
insects,  70  ;  on  absence  of  hair 
from  hrmnn  back,  and  function 
of  on  arms  of  orang,  89  ;  on 
geographical  distribution,  207, 
331,  232,  233,  243;  on  natural 
selection,  256 ;  on  recognition 
marks,  271-273;  on  alleged  de- 
ductive consequences  of  the  na- 
tural selection  theory,  273-276; 
his  theory  of  warning  colours, 
323,  324 ;  on  sexual  selection, 
391-400,  450;  his  principal 
defect  in  treating  of  animal 
colouration,  449,  450- 

Warning  colours,  323-326. 

Wasp,  imitated  by  a  fly,  329. 


Water-cress,  multiplication  of,  u 

New  Zealand,  286. 
Weevils,  on  St.  Helena,  232. 
Weismann,  his  theory  of  heredity, 

130,  134. 
Wrells,  Dr.,  on  natural  selection, 

257- 
Wetterhan,    Prof.,    on   vegetable 

galls,  448. 

Whales,  38,  50,  53,  54,  65,  180. 
Whewell,    on    natural    selection, 

257.  258,  443-445- 
Wings,  54-56,  60,  61,  68-70,355. 
Wrolf,  Tasmanian,  dentition  of,  34. 
Wood,  John,  on  vestigial  muscles 

in  man,  77- 

Woodward, on  fossil cirripedos,43 1. 
Woolner,  on  the  human  ear,  86. 
Worms,  embryology  of,  155. 
Wyman,  Prof.,  on  the  great  toe  oi 

human  embryo,  79,  80. 


Zona  pellucida,  121. 


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9.  Fundamental  Problems.     By  PAUL  CARUS.     500. 
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n.      The  Origin  of  Language.     By  LUDWIG  NOIRE.      150. 

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1 6.  On  Memory,  and  The  Specific  Energies  of  the  Nervous  Sys- 

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The  Philosophy  of  Ancient  India.     By  PROF.  RICHARD  GARBB. 
Buddhism  and  Christianity.     By  PAUL  CARUS. 
The  Lost  Manuscript.     A  Novel.     By  GUSTAV  FREYTAG. 
Old  Testament  History.     By  PROF.  C-  H.  CORNILL. 


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QH366 
RT58d 
1896 
v.l 
Romanes,  George  John 

Darwin,  and  after  Darvin 


QH366 
R758d 
1896 
v.l 
Romanes,  George  John 

Darvin,  and  after  Darvin 


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